Arjen Robben's 69th-minute goal gave Bayern a 1-0 win over Lyon in Wednesday's Champions League semi-final, first-leg, but the Dutchman was hauled off by van Gaal after 85 minutes to keep him fresh for 'Gladbach.
With second-placed Schalke playing bottom-side Hertha Berlin on Saturday, Bayern need to protect their two-point lead at the top of the Bundesliga with just three games left and need the three points from 'Gladbach.
Bayern face Werder Bremen in the German Cup on May 15 and with his side holding an advantage from the first-leg of the Champions League semi-final, van Gaal could win the treble in his first season in charge.
Robben was not amused at being brought off against Lyon and clashed with his trainer, but van Gaal said the winger has to see the bigger picture with so many important games before the season ends on May 8.
"We must play Mönchengladbach on Saturday and I had to keep him back for that game," explained van Gaal.
"No player is ever happy to be taken off, especially not Robben. "But we still have another 90 minutes of football this week."
Bayern have captain Mark van Bommel suspended after he picked up his tenth yellow card of the season in the 7-0 drubbing of Hanover last weekend.
In his absence, Philipp Lahm will deputise.
With Hertha Berlin fighting for their Bundesliga survival, Schalke need to be on their guard to keep their dreams of winning their first German league title since 1958 alive.
Hertha are five points from safety and another defeat will leave them on the brink of relegation with Bayer Leverkusen and Bayern still to come.
Schalke coach Felix Magath has nearly a full-strength side with striker Kevin Kuranyi hoping to impress with Germany coach Joachim Löw set to announce next week if he will be considered for a World Cup place.
Third-placed Werder Bremen host Cologne on Saturday night with Thomas Schaaf's side hoping to back up last week's 4-2 win over Wolfsburg with another three points to challenge for a Champions League place to finish in the top three.
Fourth-placed Leverkusen host relegation-candidates Hanover without injured Germany goalkeeper Rene Adler who fractured a rib in last weekend's defeat to Stuttgart.
Adler is expected back within two weeks, but faces an anxious wait with Löw expected to name Germany's World Cup squad on May 6.