Silvestre's injury puts Keane in line for defensive role

Manchester United have been dealt a blow after Mikaël Silvestre was ruled out for three weeks with ankle ligament damage.

The French defender limped off during the first half of Saturday's 1-1 draw with Leeds after coming off worst in a 50-50 collision with Alan Smith.

At the time the Manchester United manager, Sir Alex Ferguson, expressed his concern over Silvestre's chances of making tomorrow's Champions' League trip to Porto and his fears have been realised with confirmation of the extent of the former Internazionale player's injury. "Mikaël will be out for three weeks," Ferguson said. "It is a big blow for us but we will just have to get on with it."

The news is likely to see Roy Keane moved into a central defensive role in Portugal, almost a year to the day since he turned in an outstanding performance in that position against Juventus in Turin.

Keane notoriously dislikes the job but, with Rio Ferdinand still waiting for a date for his appeal into his eight-month ban for a missed drugs test and Wes Brown still short of full match fitness despite his substitute appearance against Leeds, Ferguson has little option.

If Keane is virtually certain to start in central defence, Ferguson's major dilemma is who to play with him.

John O'Shea has looked uncomfortable in the role this season, so the temptation may be to switch Gary Neville inside, play brother Phil at right-back and O'Shea on the left flank at the expense of Quinton Fortune, who turned in a dismal performance against Leeds.

In addition to both legs of the Porto clash, Silvestre is also set to sit out league trips to Fulham and Manchester City, plus the FA Cup sixth-round tie against the winner of tonight's replay between the Cottagers and West Ham at Upton Park.

In tonight's Champions' League games, Sparta Prague have no injury problems as they prepare to entertain Milan.

The Italian side will have to make do without the Danish striker Jon Dahl Tomasson who has a hip injury and that should give Filippo Inzaghi the chance to start alongside Andriy Shevchenko. In defence Alessandro Costacurta replaces Alessandro Nesta, who picked up a thigh strain during Milan's 3-2 victory over city rivals Internazionale at the weekend.

Lokomotiv Moscow will be without the suspended South African defender Jacob Lekgetho for their home tie against Monaco. The Russian international Marat Izmailov (back and leg injuries) is also a doubt.

The French domestic leaders will be without the injured Ludovic Giuly (foot) and Sebastien Squillaci (leg).