England international forward Rooney picked up a knee injury during last weekend’s Premier League game against Everton away from home at Goodison Park.
The 29-year-old failed to complete the entire 90 minutes and was replaced by Netherlands international striker Robin van Persie in the 88th minute.
Van Gaal has now revealed that the former Everton star has recovered from that problem and is fit to start against West Brom at Old Trafford on Saturday.
“Rooney is fit to play, it was not so heavy as we expected," the Dutchman told MUTV. "Wayne is very important for us, so I am very happy.”
On other injury concerns, Van Gaal said: “(Phil) Jones is fit but we have to see his match rhythm, of course. But (Luke) Shaw has trouble with his groin so he cannot play."
United are currently fourth in the Premier League table with 65 points from 34 matches, seven points clear of Liverpool, who are fifth in the standings at the moment.