The defender was substituted and replaced by Darren Fletcher late on in the victory, raising concerns about the teenager’s fitness, with United already short at the back.
However, Van Gaal has revealed that McNair was simply suffering from cramp and has not picked up an injury, after Juan Mata’s second-half goal handed his side victory.
Van Gaal said: “Paddy McNair is not injured. It was cramp.
“It is [the recent injury problems] crazy but it is what I have to deal with.”
The Dutchman continued: “They [McNair and Daley Blind in defence] didn’t have to defend too much because we always had the ball.
“They only had to defend the long balls but that is difficult because Marouane Chamakh and Frazier Campbell are strong headers of the ball.”
United learnt on Friday that they are set to be without Marcos Rojo for six weeks after the Argentina international dislocated his shoulder during last weekend’s 1-0 defeat by Manchester City.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news