Sir Alex Ferguson has backed Patrice Evra to quell the threat of Arsenal danger-man Theo Walcott in Wednesday's Champions League semi-final at Old Trafford.

Ferguson has set his Manchester United team the task of keeping a clean sheet in the first-leg tie as they look to move another step closer to becoming the first side to retain the trophy in its present form.

Though the Red Devils chief feels Walcott is a clear threat, he trusts his French left-back. "Patrice Evra is quick enough," said Ferguson.

"He has played against Theo Walcott a few times and been alright with that. Walcott is very quick, probably the quickest forward in England at the moment, so we will have to prepare in the right way."

Ferguson has a number of major selection dilemmas, including the other full-back position, where John O'Shea is expected to get the nod over Brazilian teenager Rafael Da Silva.

In attack it is even more of a conundrum, with Carlos Tevez's outstanding performance in Saturday's 5-2 win over Tottenham putting him in contention, along with Dimitar Berbatov, Cristiano Ronaldo and Wayne Rooney.

Wes Brown has been back in training for United while Gary Neville is said to be two weeks away with his foot injury. Only Owen Hargreaves is a long-term absentee.