Bayern Munich midfielder Franck Ribery returned to training on Monday following a knee injury that has kept him out of action for around two weeks.
Bayern are desperate for Frenchman Ribery to play against champions VfL Wolfsburg on Saturday after their worst start to the season in 43 years.
They have taken only two points from their opening three Bundesliga matches.
Bayern sank deeper down the table after two first-half goals took promoted Mainz 05 to a surprise 2-1 victory in the Bundesliga on Saturday.
Italian striker Luca Toni, who has yet to play this season, is still out with a heel injury.
Van Gaal, brought in after the sacking of Juergen Klinsmann last season, has now had a worse start than Klinsmann at the same stage last year.
"I am sure everyone saw how terrible a start we had," said Dutchman van Gaal.
"It was disappointing.
"Now myself and the team will work even harder because we know how important it is to start getting points."
