Rafael has missed United's last four matches with an unconfirmed muscle injury. Getty Images/Laurence Griffiths

Manchester United have received a massive blow in the form of injuries to full backs Rafael and Luke Shaw following their 2-0 win over League One side Yeovil Town in the third round of the FA Cup on Sunday.

Rafael had to be taken to the hospital to operate on a fractured cheekbone while Shaw was taken off at half time with an ankle injury. The current situation makes United's full-back situation extremely dire with Ashley Young and Antonio Valencia also unavailable for the 20-time Champions.

The duo are a doubt for their clash against Southampton next week, who are currently only a point behind the Red Devils and a loss here for Louis van Gaal's side will be a major blow to their hopes of securing a top four spot.

United are unbeaten in their last 11 games in all competitions but with fixtures coming thick and fast now, they need to tide over their injury crisis and push on to take their game to the next level.

Van Gaal was appreciative of Rafael's desire to play through the pain but the Brazilian could not continue as he had to be replaced at half time. It was a nervy affair for the Dutchman in his first ever FA Cup tie as second half goals from Ander Herrera and Angel di Maria sealed their qualification into the next round.

"I think we have a lot of problems in the first half, I don't think you have noticed Rafael Da Silva has an injury and a fracture of his bone so it was fantastic he had the guts to play through," Van Gaal said.

"But I have to change him and also Luke Shaw had an ankle problem so I had to change him also.

"Rafael has already gone away in a car. I don't know how he did it. I cannot say I will have to watch the video. Also, with Shaw. It was a very physical game. Rafael played through. Last few weeks he has not played so much. He has a fantastic attitude he is unbelievable."