Rio Ferdinand could miss Manchester United's clash with Liverpool at Old Trafford on Sunday.

The England defender has missed the Red Devils' last two fixtures, with Gerard Pique standing in at the heart of the United backline alongside Nemanja Vidic for the 2-0 defeat of Bolton last night.

Manager Alex Ferguson said: "Rio Ferdinand is doubtful for Sunday with a back problem.

"I had to find out about Gerard Pique. We've got great confidence in the lad and he's come through very well. They are all top players so you have to put your faith and trust in them."