Rafael, Luke Shaw suffer injuries in Manchester United's FA Cup win
Louis Van Gaal revealed Rafael suffered a suspected fractured cheekbone and Luke Shaw sustained an ankle injury in Manchester United's 2-0 FA Cup win at Yeovil.
Both defenders were withdrawn at half-time in place of Juan Mata and Jonny Evans as the Red Devils went on to win after second-half goals from Ander Herrera and Angel di Maria.
Van Gaal admitted he was forced into the changes and he praised Rafael's toughness for playing through his injury in the first half.
"Rafa has a fracture, so it's not looking good, and Shaw has an ankle problem," Van Gaal told MUTV. "I had to change, and I don't have more defenders, so I have to change the shape also.
"Rafael had a fresh injury so it was fantastic that he had the guts to play through. He has a fantastic mentality, it's unbelievable. But I had to change him and Shaw because they aren't 100 per cent fit.
"I put a midfielder extra in and, because of that, maybe we had more ball possession in the second half, and we had more patience.
"We have to change from five to four; we played four in midfield in the second half, then we played better and were more patient. We kept the ball better also and, because of that, we could score the winning goal."
With Antonio Valencia and Ashley Young currently out with thigh and hamstring injuries respectively, the injuries to Rafael and Shaw leave Van Gaal short of wing backs for his favored 3-5-2 formation for Sunday's game against Southampton.
There was some better news for United on the injury front as Di Maria completed 30 minutes and scored against Yeovil as he continues his return from injury, and Van Gaal revealed Daley Blind and Marcus Rojo are also close to returning.
"We can be very happy because the players are coming back now," he explained. "Angel di Maria is coming back, Daley Blind is coming back, Marcos Rojo is coming back.
"So we have more left-footed players, and that we need also. I have to solve every week another problem, and now during a match."