Manchester United cannot allow Saturday's FA Cup semi-final with Everton to distract them as they try to claim a top-four spot in the Premier League.
United's 1-0 victory over Aston Villa last weekend - combined with Arsenal's draw with Crystal Palace - saw Van Gaal's side move to within four points of the Champions League places.
Ahead of their cup clash at Wembley, United face Palace at Old Trafford on Wednesday, and Van Gaal has no intention of resting players given what is at stake in the final five games of the campaign.
"I don't think our players shall do that [lose focus] because they have to focus on this game because we still have to qualify for the Champions League," he told a media conference.
"It is important to beat Crystal Palace and they have the same problem. They are also in the semi-final [against Watford] and maybe they are thinking about that game. But we have to win our game against them.
"For us this game against Palace is important. We have to win, we need to win. We need to win this game more than Arsenal or Man City, they have the four-point gap.
"It is too important a game to rotate. We have to win. We can only give pressure by winning."