Manchester United suffered a massive blow after Robin van Persie got injured during the Red Devils' 2-1 loss to Swansea City on Saturday.

The Dutch striker passed a fitness test during the week after missing last weekend's game against Preston North End and returned to the starting lineup to face the South Wales club, but suffered the injury late into the game as United were looking for an equaliser after going 2-1 down.

The striker hurt himself while putting in a cross and was forced to stay on the pitch until the end of the match as Louis van Gaal had already made all three substitutions. The manager confirmed that it was difficult for Van Persie to move after sustaining his knock.

"We dominated the game even with 10 men because Robin van Persie could not run anymore after the injury," Van Gaal said, as quoted by United's official site.

It is still unknown as to the extent of the strike's injury, but the former Arsenal skipper was seen leaving the stadium on crutches with his foot in a protective boot.

Depending on the time frame of the Dutchman's injury absence, it could give Wayne Rooney a chance to play in his preferred role as a central striker as well as a continued run in the team for Colombian Radamel Falcao.

Meanwhile, the Red Devils' skipper has admitted that the defeat to Garry Monk's team is hard to take. He was disappointed in the way his team conceded the two goals, which led to Swansea completing the double on United after having beaten them on the opening day of the season at Old Trafford.

"Of course, it is hard to take. Certainly, in the second half, I thought we dominated up until they scored and I thought we got a great goal to go 1-0 up. I was really disappointed in the way we conceded, coming from a throw-in so soon after we scored," Rooney told United's official site.

"We went in at half-time knowing that we could play. In the second half they were struggling to get out but then they hit us with a sucker punch, a shot from 30 yards and a deflected goal. These things happen but it was a disappointing day for us," the Three Lions captain added.