By Paul ClennamWayne Rooney  is a doubt for Manchester United 's crunch clash with Liverpool  after sustaining a head injury in training, Goal understands. The forward left the club's Carrington base with a bandaged head after suffering the injury in training on Saturday morning.Rooney is understood to have sustained a gash, leaving the Premier League champions waiting on a medical assessment of the striker ahead of their trip to Anfield on Sunday.The striker, who has been subject to two bids from Chelsea this summer, spoke of his gratitude towards United's fans after he received a positive reaction away to Swansea and at home to the Blues during the sides' 0-0 draw on Monday. And Moyes moved to praise the former Everton star on Friday, insisting he is "mentally in good shape" ahead of the trip to face Brendan Rodgers' men. "I felt he played very well the other night [against Chelsea] and he's looking in good condition and is mentally in good shape too," Moyes told reporters."We'll do everything we possibly can to keep that going and need him to keep performing well. At the moment he's in good shape."Stamford Bridge boss Jose Mourinho has since described Chelsea's pursuit of the striker as "finished" for all parties after he secured Samuel Eto'o on a free transfer on Thursday.