Part of the skull of injured animal trainer Roy Horn has been removed to reduce pressure on his brain, according to a US newspaper.
The tigers have been the act's centrepiece for decades
The Las Vegas Review-Journal also said Horn was paralysed on the left side of his body after suffering a stroke.
Horn, part of the famous Siegfried and Roy act, was mauled by a male white tiger during a show in Las Vegas on October 3.
A spokesman for Horn said he was still in a critical but stable condition.
The newspaper quoted Lonnie Hammargren, a neurosurgeon and former lieutenant governor of Nevada, who said he had spoken to Horn's surgeon, Derek Duke.
"Dr Duke did exactly the operation he should have - otherwise Roy would be dead" the Las Vegas Review-Journal quoted Mr Hammargren as saying.
Mr Hammargren said that the tiger's mauling had caused the stroke, paralysing Horn's left side.
Siegfried says Roy does not want the tiger to be put down
"Fortunately, the stroke didn't hit on the side where he talks, thinks and remembers. He can still comprehend things and do things," Hammargren said.
Horn has been in the University Medical Centre in Las Vegas since the accident happened at the Mirage resort.
Casino entrepreneur Steve Wynn, a former Mirage owner, said last week he had seen Horn and it was unclear how he would be affected physically but his chance of survival was 95% or higher and he was mentally fit.
Horn's stage partner Siegfried Fischbacher told a US TV show last week that the tiger was protecting Horn rather than attacking him.
The German-born duo have performed in Las Vegas for 35 years.
Fischbacher said the tiger would not be put down despite the devastating injuries inflicted on his partner.
"It is Roy's wish that no-one hurts him. He will remain part of our family," he said.