People walking by La Scala Thursday evening witnessed an impromptu performance by tenor Roberto Alagna, the scorned opera singer who stormed off the famed Milanese stage when booed last weekend.

Alagna, holding a rose, delivered a few notes from Madama Butterfly in the piazza outside the famous opera house and waved to onlookers. Inside, Aida was beginning its fourth act.

French tenor Roberto Alagna waves in front of Milan's La Scala opera house, making his promised return after storming off stage on the weekend.
(Alessandro Grassani/ Fotogramma/ AP)

The French-born singer had vowed to return to La Scala, despite management's decision to cancel his engagement as Ramades in Franco Zefferelli's current production following his abrupt departure on Sunday.

In an interview Friday, Alagna blamed his mid-performance departure on a health problem.

"I was fine when I started, but this problem with my metabolism, if I am very emotional or stressed, my system consumes sugars very quickly," he said.

"I couldn't stay on my feet, I had to sit. I didn't have the strength."

Marco Rocchini, the singer's lawyer, said his client will sue La Scala for harming Alagna's reputation by not allowing him to return to the performance. He also claimed to have a doctor's certificate confirming Alagna had low blood sugar levels last Sunday night.

La Scala spokesman Carlo Maria Cella said said no certificate has been presented to the opera house's management and that Alagna had never mentioned feeling unwell.

"If a singer is sick, he goes off stage, tells the musical director and a doctor verifies the condition, we inform the audience and the understudy goes on stage," Cella said.

He added that La Scala has no plans to sue Alagna.

Video footage taken inside the opera house on the night in question shows Alagna walking off stage after being booed by a group of audience members during his opening aria, Celeste Aida. A jeans-clad understudy, Antonello Palombi, immediately rushed onstage to replace him.

The incident has made headlines worldwide, with many criticizing Alagna and others the notoriously picky La Scala audience, which has booed the likes of Luciano Pavarotti and Renée Fleming.

With files from the Associated Press