The England center-half was substituted at half-time during the Red Devils' 4-0 victory at Craven Cottage, which prompted Sir Alex Ferguson to voice his concerns.

"Rio is a concern. He went over on his ankle and we will just have to wait now and see how bad it is," the United boss told MUTV.

"I just hope he makes Wednesday because he's such an important player to us."

United already miss Gary Neville, Wes Brown and Rafael, while John O'Shea is doubtful with a hamstring injury.

However, the English champions' defensive problems are much lighter than that of their Italian counterparts.

Jose Mourinho's team have a host of defenders in their injury list, including Walter Samuel, Christian Chivu, Nicolas Burdisso and Marco Materazzi.