When Jonas Kaufmann suddenly bowed out of the Metropolitan Opera's production of "Manon Lescaut," Roberto Alagna pulled off the herculean feat of learning the complex score within days.

Alagna, France's most famous tenor, has wowed the opera world with his rapid mastery of the Puccini opera but he fears he has put his prized asset at risk -- his voice.

The 52-year-old said he spent two weeks working from nine in the morning until nine in the evening to learn the lead male role which he sings opposite Latvian soprano Kristine Opolais.

"Vocal cords start to tire after two hours. So 12 hours -- that's a lot!" Alagna told AFP in his dressing room at the New York opera house.

"It's madness. This isn't something I would do again. Because you can't control the voice, that's the problem," he said.

Alagna said he was heading to a doctor to look at a swelling in a vocal cord but did not want to sit out any performance.

Alagna has seen a career resurgence following a difficult stretch in which his failed marriage to soprano Angela Gheorghiu put him in the tabloids.

He has won wide praise for "Manon Lescaut" but insisted that he was not giving his all.

"I'm a fast study but that's not the problem. You can learn quickly but you still need time to adapt to the role on stage," he said.

"When you have so many elements and so much information to manage, you can't control your voice 100 percent. And that's dangerous, especially for such a weighty work," he said.

- A signature work -

"Manon Lescaut" premiered in 1893 and has emerged as a classic tale of illicit love, although it is less known than Puccini's next three works -- "La Boheme," "Tosca" and "Madama Butterfly" -- which have become some of the world's most loved operas.

Based on the novel by Abbe Prevost that caused a stir in 18th century France, the femme fatale title character is shipped first to a nunnery by her father and eventually into exile in colonial Louisiana for her brazen sexual openness.

In the Met production by British director Richard Eyre, "Manon Lescaut" is set anachronistically in the 1940s with German troops in control of France, the stage assiduously designed to evoke a grand Parisian home.

The Met had heavily promoted the chemistry between Kaufmann and Opolais, with printed programs offering insights into their dynamic. But Kaufmann, one of opera's biggest box office draws, withdrew citing illness weeks before the February 12 opening.

Confounding the crisis, "Manon Lescaut" was slated for "Live in HD," the Met's broadcasts in cinemas around the world.

"Live in HD" has emerged as a vital revenue generator for the Met and Saturday's broadcast of "Manon Lescaut" will mark the milestone of 20 million tickets sold since the broadcasts began in 2006, according to the opera house.

- No rest in sight -

Alagna said that the Met's general manager, Peter Gelb, asked him virtually on the spot to accept the role, not giving him the customary time to reflect on the score.

Alagna had some familiarity with "Manon Lescaut" as he planned to join a 2006 production in Turin, but he canceled due to illness before trying to memorize the score.

"I did this because they were facing an enormous problem. They had a costly production and HD and they didn't have anyone," Alagna said.

"They told me it was truly a disaster for them. It was the first time I ever saw Peter Gelb so perturbed," he said.

Alagna was already in New York for "Pagliacci" and later this month takes on yet another Met role, in "Madama Butterfly."

He has little rest on the horizon, with upcoming concerts in Paris and Bogota and an album in the works named for his beloved two-year-old daughter, Malena.

He is also learning another new role -- "La Juive," in which he will again star opposite Opolais starting in June in Munich.

"I enjoy pushing myself to the limits, but I also need to be careful," he said.