Silvestre blow for Man Utd

Silvestre was injured against Leeds

Manchester United have suffered another defensive setback with the news Mikael Silvestre will miss the next three weeks with ankle ligament damage.

The French defender limped off during Saturday's 1-1 draw with Leeds after a clash with Alan Smith.

"It is a big blow for us but we will just have to get on with it," said United boss Sir Alex Ferguson.

He is already without Rio Ferdinand and Gary Neville through suspension and Wes Brown is still short of match fitness.

United's defensive short-comings have been exposed in recent weeks, as they have slipped behind Arsenal in the Premiership title race.

And Silvestre's absence will lead to further reshuffles at the back for Ferguson, as United's Champions League campaign resumes this week with a match against Porto.

Match report: Man Utd 1-1 Leeds Utd

Skipper Roy Keane looks set to drop back into a central defensive role in Portugal on Wednesday - almost a year to the day since he performed heroics in that position against Juventus in Turin.

Midfielder Keane famously dislikes the centre-back's job - but Ferguson has few alternatives.

Ferdinand is still waiting for a date for his appeal into his eight-month ban for a missed drugs test and Brown has struggled since returning from a long lay-off with a cruciate ligament injury.

Gary Neville may switch from right-back to the centre for the Porto clash - but the England international will then start a four-match domestic suspension for head-butting Manchester City's Steve McManaman.

In addition to both legs of the Porto clash, Silvestre will also miss Premiership visits to Fulham and Manchester City, plus the FA Cup tie against the winner of Tuesday's replay between Fulham and West Ham at Upton Park.