By PATRICK HEALY

WHEN a team of Broadway veterans began pitching New York producers on turning the classic 1976 movie “Rocky” into a musical, the mere idea made people wince. Would it have a chorus of tap-dancing boxers? Fighters breaking into song in the ring? A musclehead made eloquent with rhyming lyrics, as he punches sides of beef in a meat locker?

“People couldn’t believe we didn’t see it as satire,” recalled the composer, Stephen Flaherty (“Ragtime”), one of several Tony Award winners developing the project.

Recruited by a very determined Sylvester Stallone, the original Rocky himself, Mr. Flaherty and his collaborators never tried to go the fashionable route of a winking sendup, like the musical “Xanadu.” But the chilly reception from Broadway backers knocked out “Rocky” until, the lyricist Lynn Ahrens said, “these crazy German people showed up.”

They were executives from Stage Entertainment, the leading European presenter of musical spectacles like “The Lion King” “Mamma Mia!” and “Tarzan.” And they came eager to grow their multimillion-dollar empire — which specializes in retrofitting Broadway musicals (even flops) for audiences in Hamburg, Madrid, Paris and elsewhere into their native languages — and to develop more shows on their own. If “Rocky the Musical” struck some as the dumbest movie-to-musical yet, following recent Broadway flops like “Ghost” and “Leap of Faith,” “Rocky das Musical” held promise as the sort of testosterone-fueled event that can whip German audiences into a lather.

A chance encounter between Stage executives and Mr. Stallone led to a transatlantic collaboration, with script readings and boxing workshops in New York, and months of German-language translation revisions in Hamburg, where “Rocky das Musical” opened Nov. 18 in a $20 million production — one of the most expensive ever. The reviews have been rapturous from critics here, and now its producers are eyeing a possible production on Broadway. Yet they are proceeding warily: while Hamburg has become a profitable hub for New York musicals, even called “the Broadway of Europe” in some circles, this tourist-heavy city has mostly been an importer of shows during its curiously meteoric rise as a musical theater capital.

Whether Broadway-caliber tastemakers will emerge along the red-light district of the Reeperbahn here, where “Rocky” is playing across from sex-and-kino parlors, is among the questions facing the show.

“We know New York right now is one step higher artistically and commercially than Europe,” said Joop van den Ende, the founder and owner of Stage Entertainment, who has invested in 15 shows on Broadway since 1993 and was the lead producer of “Sister Act,” which closed in August without turning a profit. “There is much work to do to make ‘Rocky’ better and better. But people in New York will be pleasantly surprised by what we have.”

And, perhaps, surprised by what the show doesn’t have.

While its plot hews to the first “Rocky” movie — a $1 million picture that earned $225 million worldwide, won the Academy Award for Best Picture and spawned five sequels — the musical has relatively little boxing and no awkward attempts to meld prizefighting with high kicks or hoofing. Nor does the American actor playing Rocky, Drew Sarich, have the sagging lip or body mass of Mr. Stallone. And his performance is imitation free. (Mr. Sarich described his Rocky as “a Rottweiler puppy who hasn’t grown into his paws.”)

The set and lighting design are imaginatively low key: The bare stage at the Operettenhaus Theater here becomes a grimy, cavernous gym; rectangular, boxlike settings for the working-class homes of Rocky and his girlfriend, Adrian, slide on and off stage; and a regulation-size boxing ring appears for Rocky’s climactic fight against Apollo Creed, which includes a startling coup de théâtre.

Blending big-budget flourishes and Off Broadway experimentation is part of the aesthetic of the “Rocky” director, Alex Timbers, himself a Tony nominee whose shows “Bloody Bloody Andrew Jackson” and “Peter and the Starcatcher” moved from downtown New York to Broadway. Mr. Timbers, who was born two years after the original release of the film, said that his goal for “Rocky” was to combine “the intimate and the epic — the indie-movie sensibility of watching two people in a room, then pack in a gladiatorial feel where the emotions fly.”

“We’ve tried to think of this as an indie musical — the David Fincher version of ‘Rocky,’ ” he explained. “And scale some of the scenes and sets to fit the human beings you’d see in a Sam Shepard play.”

When Mr. Timbers signed on to direct in 2011 — after initially telling his agent that the idea “had a 95 percent chance of being awful” — he became the latest in a string of converted skeptics (and well-paid ones, given the spare-little-expense approach of the producers). The first artist wooed to the project was Thomas Meehan, the Tony-winning book writer for the hits “Annie,” “The Producers” and “Hairspray,” whom Mr. Stallone contacted through a mutual lawyer. During their first meeting at Mr. Stallone’s hacienda-style home in Beverly Hills, Calif., the two men watched “Rocky” and Mr. Stallone explained his vision: that the movie was, at its core, a love story between two lonely people who struggle to express themselves and ultimately persevere because of each other.

“I imagined it in the style of a ‘West Side Story’ or a ‘Saturday Night Fever,’ with these almost childlike characters who the audience will want to root for,” Mr. Stallone said. “But I knew it had to be gritty, street smart. And that it couldn’t be too — what’s that word in musical theater? It couldn’t be too exuberant.”

Mr. Meehan went to work on the script — Mr. Stallone wrote the original, Oscar-nominated screenplay reportedly in three days — and the two began talking to songwriters. At first Mr. Stallone wanted a Hollywood artist like Diane Warren; later, he and Mr. Meehan even flew to Chicago to trade ideas with R. Kelly. Mr. Meehan eventually persuaded Mr. Stallone to hear music from a Broadway team like Ahrens and Flaherty, and then began another sales job on the songwriters.

Asked what she first thought about a musicalized “Rocky,” Ms. Ahrens replied, “Honestly?” Laughing, she continued: “Stephen and I were both like, ‘No way.’ We just couldn’t imagine what it would be. And actually I hate boxing. The violence. But my husband loves ‘Rocky,’ and he just said, ‘Lynn, read the script, have an open mind.’ ”

Several songs they first played for Mr. Stallone in 2006, as he was in Philadelphia filming the most recent movie sequel, “Rocky Balboa,” are in the musical, like “Fight From the Heart," Rocky’s big Act I number, in which he tries to imagine advice from his hero, Rocky Marciano. That song is one of several power ballads in the show, which also interweaves the famous Bill Conti movie theme and even the hit song “Eye of the Tiger” from “Rocky III.” (For Broadway, Mr. Stallone said he hopes to add in the James Brown song “Living in America,” which was featured in “Rocky IV.”)

Most of that inspirational movie music accompanies the musical’s boxing scenes: a down-and-dirty fight at the beginning and then the 15-minute fight at the end, which features full-contact punching.

Steven Hoggett, the Tony-nominated choreographer (“Once”) known for highly physical work (the boxing play “Beautiful Burnout,” “Black Watch”), said he wanted the boxing to look as real as possible — without injuring actors. Once he trained them in the traditional stance and four basic punches, Mr. Hoggett created the final fight, which mixes plenty of flying sweat and bloody gashes with the song reprises, which all but Rocky and Apollo sing.

“The trick of a show like this is, you say you’re turning ‘Rocky’ into a musical, and people will think it’s lightweight,” Mr. Hoggett said. “So the tone of everything has to convey strength and precision.”

Posing a major challenge to the creative team was that none of them spoke German. (“All I understand is when Rocky says ‘Yo,’ ” Mr. Stallone said.) The language barrier forced Mr. Meehan and Ms. Ahrens to depend on translators to shape the dialogue and lyrics, and in doing so, rein in their own tendencies as incorrigible perfectionists. While shows like “The Lion King” were refined into hits in English-speaking theaters before they were translated into German, “Rocky” has not been staged in English, so its creators have to rely on gut instincts, making changes based mostly on audience reaction here.

“It’s pretty difficult to make writing changes on the fly, because, for instance, there’s no real slang in German,” Ms. Ahrens said. “The words ‘My nose ain’t broken’ is the actual English line of a song, but there isn’t slang for that in German — and it wouldn’t fit in the music anyway. So with our German translator we came up with, ‘My nose is still standing,’ and then worked on that.”

Mr. Timbers, for one, has picked up some German during several months of working here, and the audience at one preview performance last month was audibly pleased when he welcomed them from the stage with a simple “Guten abend!” But as it does at many musicals, audience feedback at “Rocky” has come through body language: the laughter as Rocky shambles through early scenes with Adrian, the clapping to the Conti music and some other songs. (A spokesman for Stage Entertainment whispered during one song, “Germans love to clap along.”) Several theatergoers said during intermission that they were particularly excited to see a boxing musical onstage, given the sport’s popularity in Germany, though a couple of people were disappointed that there weren’t more punches thrown.

If the creative team has been pleased by the response to the show — and admittedly relieved that it was not regarded as a desecration of “Rocky” — the producers at Stage Entertainment have been ecstatic. Broadway producers say they have been invited here to see the show — hardly a guarantee of a New York transfer, given the skepticism surrounding a “Rocky” musical, but a step in that direction.

“People didn’t believe this show could work, just like people didn’t believe in Rocky,” said Johannes Mock-O’Hara, the company’s managing director for Germany. “But both the show and the man are about believing in yourself.”