The German champions have made a slow start to the Bundesliga and Van Gaal said they were still feeling the effects of a short preparation for the season, a result of the World Cup in which a number of their players played a prominent role.
"It's always difficult when a team has a lot of players at the World Cup and they cannot enjoy a good preparation," the volatile Dutchman told reporters. "This year was a very extreme case.
"So we had to do our preparations by playing in the Bundesliga, the German Cup and the Champions League, and that is naturally a bad thing."
The World Cup finished on July 11, barely a month before the start of the German season.
Philipp Lahm, Bastian Schweinsteiger and Thomas Muller helped Germany to finish third in South Africa while captain Mark van Bommel and winger Arjen Robben played in the Netherlands side which lost to Spain in the final.
Defender Martin Demichelis was in the Argentina side which reached the quarter-finals.
Robben has missed the start of the Bundesliga season, angering Bayern who say he aggravated an injury by playing in South Africa.
Bayern are a modest ninth in the Bundesliga, having taken eight points from six matches, and are already 10 behind leaders Mainz 05, who beat them 2-1 on Saturday.
The Bavarians also began last season slowly but underwent a dramatic change after beating Juventus 4-1 away to reach the last 16 of the Champions League.
Van Gaal, who led Bayern's Bundesliga celebrations with an unforgettable speech from the balcony of Munich's town hall, said he hoped Tuesday's Champions League match at Swiss champions FC Basel could provide a similar springboard.
"If we win really well, that could be a turning point, the same thing happened with the Juventus game last season," said Van Gaal, whose team beat AS Roma 2-0 in their opening group match two weeks ago.
He added: "In five of our Bundesliga matches, we have played well, we have always been the better team and we created more chances, but we are not finding it easy to score goals."
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