The Germany international, who was the top scorer at the World Cup last summer, has been dropped from the Bayern first team recently and Van Gaal has no intention of bringing him back purely on past reputation.
"Muller's performances have not been good recently," said the Dutchman. "He will have to wait for his chance because the others have been doing really well.
"He seems a bit burnt out, more mentally than physically."
Muller has also been left out of the Germany squad for a friendly against Sweden next week and will therefore be given time to recharge his batteries before making a return in the Champions League tie with Roma in 10 days time.
That is when Mark van Bommel, Breno and Franck Ribery should also make their returns to action.
"It is still too early," explained Van Gaal. "Having 19 fit players does not mean that they are all actually fit to play. I cannot give everybody 90 minutes.
"We have the games against Rome and Basel available to give these players match practice."
Sunday's Bundesliga game is too important to take any risks.
Rivals Nurnberg are two points above Bayern in the league while the gap to the summit has increased to 15 points after Borussia Dortmund's win over Hamburg last night.
"It currently looks like Dortmund are favourites for the title," admitted Van Gaal, who had a dig at tomorrow's opponents.
"Nurnberg are only so strong because they loan players from Bayern Munich. If we win, then we go ahead of them and that is very important for us."
Mehmet Ekici is the only remaining Bayern player still on Nurnberg's books after Breno and Andreas Ottl both returned to Munich in the summer.
"The deal is that he spends a year here and then goes back to them, but the competition for places at Bayern is higher than it is here," said Nurnberg coach Dieter Hecking.
"Maybe he will stay here another year. The move to Nurnberg has done him good."