Valencia injured his hamstring during Sunday's 2-1 win over West Bromwich Albion, the Manchester Evening News reports. "This is what I call a December injury," manager Jose Mourinho said. "It is an injury of accumulation of fatigue. It is a muscular one. Hamstring. Big, small, medium, I don't know. Let's wait. I think he is an experienced guy to not let it go to difficult limits."