Tottenham midfielder Sandro has undergone a knee operation.
The Brazil international was injured during the first half of the 0-0 draw against QPR at the weekend.
And a short statement on the club's website confirmed surgery was required to repair an unspecified problem.
It read: "Sandro has undergone knee surgery following the injury that forced his substitution against QPR at the weekend. The midfielder's recovery schedule will be assessed over the next few days."
Sandro later wrote on his Twitter page: "My surgery went well, now its moving forwards with treatment and rest. Many thanks to everyone for their support - I'll be fine to fight again."
Andre Villas-Boas suggested in the immediate aftermath of Saturday's game that Sandro's injury was not serious.
He said at the time: "He should be okay for the Manchester United game next week. It's just a knock on the knee."