Manchester United beat West Bromwich Albion 2-1 on Sunday but the win came at a cost as Antonio Valencia limped off in the second-half and Jose Mourinho admitted he was in the dark over the period the fullback is expected to missing in action for.

“This is what I call a December injury. It is an injury of accumulation of fatigue. It is a muscular one. Hamstring. Big, small, medium, I don’t know,” Mourinho said at his post-match press conference.

Mourinho was asked how long the right-back is expected to be out of action, to which he responded: “Let’s wait. I think he is an experienced guy to not let it go to difficult limits. But it is an injury of fatigue. Everyone in the Premier League especially the ones in more accumulation of cups, European cups, they are at risk”.

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Valencia had been captaining United with regular skipper Michael Carrick sidelined due to heart problems and the Ecuadorian was in fine form this season, scoring two memorable goals for the Red Devils.

The hard-working South American played twice in the UEFA Champions League but was an ever-present in the Premier League as he started in all 18 of United’s games.

United next face lower-league side Bristol City in a EFL Cup quarter-final on Wednesday before visiting Leicester City for a Premier League fixture on Saturday and Valencia’s absence will be keenly felt as the fixtures continue to come thick and fast.

The Red Devils, who are in second place in the Premier League, will hope the 32-year-old isn’t out for long as they will need all hands on deck in the weeks to come.

Currently, United have Carrick (heart), Marouane Fellaini (knee), Eric Bailly (ankle) on the casualty list while star midfielder Paul Pogba is serving a three-match suspension.