Manchester United was dealt a major form winger Antonio Valencia will sit out for a month with a hamstring injury.

Valencia, 26, sustained the injury in the build-up to Javier Hernandez's 85th- minute goal and was immediately substituted.

"He has a hamstring injury unfortunately," said United manager Sir Alex Ferguson after the match. "It will be four weeks. It's a blow to lose Valencia, but bit by bit we are getting stronger with Nani and Ashley Young coming back."

The Ecuador international will sit out the return leg against Ajax at Old Trafford and is also expected to miss key Premier League tilts against Norwich City and Tottenham.