Louis van Gaal has confirmed that Wayne Rooney will miss Manchester United's Europa League first-leg clash against FC Midtjylland with a knee problem, but refused to confirm reports his captain faces two months on the sidelines. The Dutch manager lamented the news which leaves him with 13 absentees for the trip to Denmark, including Matteo Darmian, Cameron Borthwick-Jackson, Marouane Fellaini, Bastian Schweinsteiger, Phil Jones, Guillermo Varela and long-term absentees Antonio Valencia, Ashley Young, Luke Shaw and Marcos Rojo.

Rooney, who has scored seven in his last nine appearances for United, played the full 90 minutes during the 2-1 defeat to Sunderland at the weekend. However, fears began circulating when United issued a statement saying the striker will miss the Midtjylland trip, adding: "The manager is expected to confirm why his captain has not made the trip during his pre-match press conference."

Reports suggested that Rooney will be out of action for two months with a knee ligament injury. Van Gaal has now confirmed that his captain has injured his knee, but refused to confirm his projected absence period.

"We have 13 players injured and Wayne is one of them," the boss confirmed to MUTV, "You can never say [how long he could be out for]. He has a knee problem so we have to wait and see. He scores a lot of goals so he is very important for us. We know that but we have to cope with that."

Asked later in the press conference to set a deadline for his recovery, Van Gaal added: "It's difficult to say but he was injured in the game versus Sunderland and has a knee problem. We have to wait and see how long that takes. I cannot say.

"Certainly in 2016, he has scored and that's why we had a good run of matches until Sunderland. But we have to cope with that. Everybody can be injured and also the captain can be injured."

The Dutchman believes Rooney suffered his injury at the Stadium of Light, despite playing the full 90 minutes.

"That's also typical Wayne. He's a guy who wants to go until the end and if he is feeling pain, he doesn't want to go away, and certainly when you are drawing a match because he wants to win. That's a fantastic attitude but also it's bad for his body. You do not know when it happened, so that's the difficulty."

If the captain does miss two months, it would mean a major blow for the Red Devils' hopes of making the Premier League top four, as the captain will miss crucial games against Arsenal on 28 February, Manchester City on 20 March and Spurs on 9 April.

Matteo Darmian and Borthwick-Jackson, meanwhile, have also been ruled out of the trip to Denmark. The Italian dislocated his shoulder during the defeat at the Stadium of Light, and the youngster is ill. Donald Love, 21, has been included in the squad after making his debut against Sunderland.

"Darmian has a dislocated shoulder, it's not the heaviest type so we are lucky, but he is injured and out," the boss said. "Cameron Borthwick-Jackson is ill and cannot play either, so we have 13 players injured or not capable of playing.

"Our policy was not to have a big squad as we wanted to try youngsters in our team. Normally we don't have 13 injured players. It's ridiculous when you analyse it – they're all contact injuries. With that policy, once or twice you have to back up the team with youngsters but injuries have happened every week this season."

Van Gaal, meanwhile, confirmed that Fellaini has also missed the the trip to Midtjylland due to a muscle problem. "Fellaini is injured. It's a muscle problem because he has played a lot of matches in a row, which is difficult for him."