The 19-year-old has started two Premier League games for United this season – against West Ham and Everton – with the Red Devils taking the three points on both occasions.
Van Gaal could be forced to call on McNair again against Crystal Palace on Saturday after Marcos Rojo was ruled out for six weeks with a dislocated shoulder.
And speaking at his weekly news briefing on Friday, Van Gaal said: “With him, we have played two victories in a row, so maybe he is the key for our success!”
The United boss also hinted that he may use teenager James Wilson more often this season.
When asked by MUTV if Wilson was pressing for a second start in the Premier League, Van Gaal said: “From what I have seen this season, [yes], but he was also injured a few times.
“He has already been knocking on the door for a long time, that I have said in many press conferences.
“That is not only because he substituted Robin van Persie in the last match. I believe in him but he has competition with [Radamel] Falcao and Robin van Persie.”
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