LONDON, March 21 (Reuters) - Manchester United could be without centre-back Rio Ferdinand for Sunday's top-four encounter with Liverpool at Old Trafford (1330 GMT).
Ferdinand, who missed Wednesday's 2-0 win over Bolton Wanderers, is hoping to shake off a back problem.
Goalkeeper Edwin van der Sar, who missed the matches against Derby County, last weekend, and Bolton with a groin strain could return.
Liverpool, who have won their last seven league and cup matches, are without long term absentees Daniel Agger (ankle) and Andriy Voronin (knee), while defender Steve Finnan (hamstring) is still doubtful after missing the last five games.
