Roy Keane is unlikely to play again this year after aggravating a knee injury during the Republic's victory over Iran on Saturday, which will almost certainly require surgery.

Medics at Manchester United had hoped that the injury - damage to Keane's patella ligaments originally sustained four weeks ago in the warm-up for a game against Deportivo La Coruna - would heal naturally given rest.

After missing five games for his club, Keane played the whole of Saturday's World Cup qualifying play-off but felt the effects immediately and returned to Manchester rather than join the Republic squad in travelling to Tehran for the second leg. He spent yesterday undergoing a series of tests and scans to ascertain the extent of the damage. The news will come as a disappointment to Alex Ferguson as he tries to rebuild United's faltering season, but was not entirely unexpected. Ordinarily Keane would have been withdrawn from international duty as a precautionary measure, but given the importance of the tie, and Keane's status as Ireland's captain, an exception was made.

Meanwhile, United's French full back Mikael Silvestre has denied reports that he expects to leave the club, insisting that he was misquoted. Several journalists in Melbourne, where France played Australia on Saturday, quoted Silvestre as saying he "could be leaving by Christmas". But he wrote on his website yesterday that "this is totally wrong. I think the translation went wrong. I have no will to leave Manchester United."