Italian conductor Riccardo Muti has walked out of an upcoming production at the Royal Opera House in a row over set design at the London venue.
Riccardo Muti has been La Scala's music director since 1986
Muti, musical director of La Scala in Milan, pulled out of Verdi's La Forza del Destino when the Royal Opera House requested changes to the set.
The production will go ahead with Tony Pappano, the Royal Opera House's own music director, holding the baton.
Chief executive Tony Hall described the situation as "galling".
"Why in this case minor changes [to the set design] should prove so difficult to accept bemuses us all," he said on BBC Radio Four's Today programme.
"Muti refused to engage in debate and didn't grace us with his presence."
He added that it was unlikely the Italian maestro would be invited back to the Opera House "in the next three to four years".
Muti's seven guest appearances in October and November conducting La Scala's production of La Forza was one of the highlights of the Royal Opera House's 2004 programme.
But problems arose when the Royal Opera requested changes to some pieces of set that had been shipped over from Milan.
The Royal Opera House said the four sections of metal wall were too heavy to hang in its fly tower and would breach health and safety rules.
To reduce their weight, it partly remade the scenery from cloth without changing their colour or design.
However, Hugo De Ana - the production's Argentinean director-designer - refused to sanction the changes.
Muti sided with his director and withdrew from the production, forcing Pappano to step in at short notice and learn the score from scratch.
"Our music director has been a hero," said Mr Hall. "He's had to cancel some performances in Chicago which has disappointed audiences there.
"But I have no doubt that with Tony Pappano conducting and Maestro Muti's cast it's going to be a great event as well."
The opera will go ahead as planned, though Covent Garden will not be able to describe it as a La Scala production.
A spokesman for the Milanese opera house said Muti and De Ana had decided to withdraw because the new production was "not completely faithful to their conception".
Tony Pappano joined the Royal Opera House in 2002
He added that the decision "upholds the tradition of La Scala that any restaging corresponds absolutely to the original production".
However, he said that La Scala hoped "there may be a fresh opportunity to work together with the prestigious British Opera House".
That seems unlikely given the tone of the joint statement released on Thursday by Mr Hall, Mr Pappano and Elaine Padmore, the company's director of opera.
"Maestro Muti does not accept what we think are minor scenic changes which need to be made to the production for it to fit safely on the Covent Garden stage," it read.
"We are totally perplexed by Maestro Muti's last-minute decision given the level of co-operation, goodwill and trust shown by the Royal Opera House towards the Maestro and the Teatro all Scala."
La Scala is nearing the end of a three-year refurbishment and is scheduled to re-open in December.