Antonio Valencia looks set for a spell on the sidelines after Jose Mourinho confirmed that the defender had suffered a hamstring injury following Manchester United's 2-1 win over West Bromwich Albion on Sunday (17 December).
The Ecuadorian, who has captained the Red Devils this season in the absence of Michael Carrick, limped off in the 66th minute and was replaced by Marcos Rojo. United were leading 2-0 at the time, and held on despite a late charge by the Baggies.
Valencia's absence will come as a blow to Mourinho's side, as it follows confirmation that Eric Bailly could miss up to three months owing to an ankle injury, that now requires him to go under the knife. Ashley Young could replace the Ecuador international at right wing-back or even at right-back after being deployed in the left side earlier this season.
Mourinho believes the injury is the result of fatigue owing to the hectic schedule in recent weeks. Valencia has made 21 appearances across all competitions for the Red Devils, and depending on the extent of the injury, which is yet to be revealed, he could face a spell on the sidelines for between two to four weeks.
"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 after United's win, as quoted on the Red Devils' official site.
"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," the Portuguese coach added.
Mourinho, meanwhile, defended Lukaku's decision not to celebrate after he had given United the lead in the 27th minute. It was his second goal in as many games against the team he played for during the 2012/13 campaign.
The Belgian refused to celebrate and the Red Devils boss believes that the striker still holds fondness for the Baggies, with whom he had a successful loan spell scoring 17 goals in 35 appearances.
"I didn't celebrate too. Nobody was happier than me. Fifteen years ago I look at myself celebrating goals. With maturity you go into levels that you control your emotions better. Romelu was a happy kid at West Brom (on loan during the 2012/13 season) – maybe at the back of the mind it was his love for the club," Mourinho said talking about his lack of celebration and the striker's.