Michael Essien

Michael Essien could miss crucial Premier League and Champions League games for Chelsea after suffering what appears to be a serious knee injury while on international duty with Ghana.

The 25-year-old midfielder was forced out of his country's 1-0 World Cup qualifying defeat by Libya, at the Stade 11 June stadium in Tripoli on Friday night, after a crude challenge midway through the first half.

Essien was replaced, after 22 minutes, by Ghana captain Stephen Appiah - who was making his first appearance in a competitive match after a nine-month absence because of injury - and flew back to London yesterday, where he was due to be examined by the club's medical staff.

With a Premier League visit to Manchester City - poachers of Chelsea transfer target Robinho - on Saturday, followed by home games against Bordeaux, in the Champions League on 16 September, and Manchester United, on 21 September, Blues manager Luiz Felipe Scolari will be hoping for good news from the treatment room.

It was a knee problem that forced Essien to miss the opening match of Chelsea's League campaign, against Portsmouth, and he then played against Wigan and Tottenham when not completely recovered. Chelsea's other holding midfielder,