The Red Devils face Everton at Goodison Park in the Premier League on Saturday evening.
The 20-time English champions travel to Russia to face CSKA Moscow in their third Champions League group-stage fixture.
United finish a tough week with a home fixture against their bitter derby rivals Manchester City at Old Trafford next weekend.
Speaking at his pre-match media conference on Friday afternoon, Van Gaal discussed a tough week for the Red Devils across two different fronts.
“It’s a big challenge because we have to compete in different competitions,” Van Gaal told his pre-match media conference.
“Everton has always been difficult for United in history, then Moscow [is in] the Champions League at the highest level.
“Then we have to play against our competitor, City. It is a very heavy week so we have to be prepared for that. After an international break it is not easy.”
United dropped to third place in the Premier League table after a 3-0 loss to rivals Arsenal at Emirates Stadium before the international break.
The Red Devils have collected 16 points from a possible 24 after eight Premier League games this term.
The 20-time English champions haven’t won at Goodison Park since 2011, losing three successive games.
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