Erik ten Hag says Manchester United have launched an internal investigation into their debilitating injury list this season after defenders Lisandro Martinez and Victor Lindelof became the latest casualties.

United have suffered continuous setbacks throughout the campaign with under-pressure boss Ten Hag often unable to field his strongest line-up.

The crisis deepened this week with defenders Martinez and Lindelof ruled out for a month with calf and hamstring injuries respectively, joining Luke Shaw and Tyrell Malacia on the sidelines.

Asked why United were suffering so many injuries, Ten Hag said on Wednesday: 'We have an idea but we will work on that internally and deal with it.'

Raphael Varane and Jonny Evans have eased United's injury problems at the back ahead of Thursday's Premier League visit to Chelsea. 

Varane also went off at the interval but has recovered in time to face Chelsea, and Evans also returns after missing the last two games with a calf injury. 

There was more good news for United when Harry Maguire, who replaced Varane at Brentford despite doubts over his fitness, trained on Tuesday.

'There are no more issues, we don't need any!' said Ten Hag. 'In the front line and midfield we are okay and we have options there, but in the back line we have a lack of options. 

'The good thing is back that Rapha Varane and Jonny Evans are in training this afternoon. Yesterday Harry Maguire was back in training.'

Ten Hag blamed United's persistent injuries on an 'overload' of games and pointed out that other Premier League teams have suffered as well.

'You can't prevent it, it's not only us who've had this,' he added. 'The standards of the Premier League from an intensity perspective are so high, the overload of the schedule, international football is so huge, and we have internationals in our squad.

'Man City, Liverpool and Newcastle have problems, many other teams. We don't train because we recover then you go up to the next game.'