Erik ten Hag has said Manchester United remain unsure why they have sustained so many injuries despite conducting an internal investigation. The manager has been without up to 11 players owing to various problems this season, with Casemiro, Lisandro Martínez, Tyrell Malacia, Harry Maguire, Mason Mount, Kobbie Mainoo and Victor Lindelöf absent for Saturday’s early kick-off at West Ham. Christian Eriksen, Amad Diallo, Luke Shaw and Raphaël Varane have previously been missing. Ten Hag said: “We did research about it but there are so many factors, you can’t point at one factor. But in this moment what is most important is that we have to deal with it and we have to work to get the players back as soon as possible because we know we have a strong squad once we have everyone on board.” He was asked whether the investigation offered hope of being able to reduce the future number of injuries. “Sometimes it can also be bad luck,” he said. “What definitely hurts was that in crucial positions we had problems. Like now in the centre-backs, so it’s not only one, there are many injured. Left full-back, we struggled for a long time this season – Luke Shaw and Tyrell.” Ten Hag then referenced accusations, which the player denies, made in Brazil against Antony, as well as other players’ injuries: “Then on the right wing we had our problems, around Antony and also Diallo in the same moment so we struggled a lot in such key positions. Don’t forget Casemiro – he is a huge impact player for us and now over a long period he is not available. You have to deal with that but everyone understands that when key players are not available it will have a negative effect on results. Still we are in a place where we can change the story, change the season.” Ten Hag said he still did not know whether his first-choice goalkeeper, André Onana, would be absent in January as part of Cameroon’s Africa Cup of Nations squad. “I can’t answer this question at the moment but if they call him up you know the regulations,” he said. The winter break means United have only two matches scheduled for next month – the FA Cup third-round game at Wigan on Monday 8 January and the Premier League visit of Tottenham the following Sunday – though the Cup tie could go to a replay and the fourth round is set for the weekend of Saturday 27 January.