Manchester United boss Sir Alex Ferguson has explained Cristiano Ronaldo's bizarre substitution during last night's 1-0 win over Sunderland.

Ronaldo is a doubt for Saturday's match against Tottenham after suffering a heavy bang on his hip which eventually saw him leave the field in bizarre fashion, the Ballon D'Or winner booting the ball out of play and then walking to the touchline before Ferguson had a chance to even get a substitute stripped.

"He got real kick on the hip-joint, just like Wayne Rooney did last year when he was in pain for a while and missed a couple of games," said Ferguson.

"We will see what he is like tomorrow, although I was going to make changes for the Champions League game against Aalborg on Wednesday anyway."