Tenor Roberto Alagna has threatened to sue La Scala if the opera house does not let him return following his abrupt stage exit during a performance.
The Franco-Italian singer, who was playing a leading role in Verdi's Aida, walked off after being booed.
His understudy had to take the stage wearing jeans for the show to continue.
The opera house management said he would not sing the remaining scheduled performances as he had technically broken his contract.
"His behaviour has created a rift between the artist and the audience, and there is no possibility of repairing this relationship," spokesman Carlo Maria Cella said.
"He did not leave because he was sick; he left voluntarily."
Alagna contacted the opera company to tell them he was ready to return but was told his contract had been annulled.
He accused La Scala of treating him like "a monster" and had contacted his lawyers to sue the company.
"I went there to sing, to give the audience joy and pleasure," he told Reuters news agency.
"But what was I supposed to do when some people started booing? What if they had thrown stones at me or some crazy person had attacked me?
"La Scala should have protected me, the show should have been suspended."
Last Thursday's production saw a star-studded audience - which included Italian Prime Minister Romano Prodi and German Chancellor Angela Merkel - welcome in La Scala's new season.
But while it received a standing ovation reviews of Alagna - playing Radames, the Egyptian commander who must choose between his love for the slave Aida and his loyalty to the Pharaoh - were less than kind.
And it was during the second night's performance that Alagna was booed, causing him to vacate the stage.
Understudy Antonello Palombi was then forced to take the stage without warning, valiantly taking over the role, minus his costume.