The Manchester United manager today revealed both Robin van Persie and James Wilson were struck down with a virus in the week.
Both forwards missed United's trip to Crystal Palace, where the team came from behind to win 2-1 and end a three-game losing streak in which they hadn't managed a single goal.
As did Angel Di Maria, who was injured for the clash at Selhurst Park following a knock in training on Wednesday.
On the virus, he said: "The manager is touched, Van Persie is touched and also Wilson last week.
"But a lot of players have problems, and also members of staff, so it's not easy to make a line-up.
"Di Maria was injured in training on Wednesday."
The Dutchman's injury worries were worsened still in south London this afternoon when left-back Luke Shaw was stretchered off.
Shaw, 19, has missed the vast majority of the season due to fitness problems and appeared to hurt his neck in a challenge with Glenn Murray.
The England international was brought off just 35 minutes into the game and, on the stroke of half time, Wayne Rooney hobbled to the sidelines with a muscle problem.
It is not known how long - if at all - the five new casualties will be out for but Van Gaal may have a headache when selecting a team for their remaining games against Arsenal and Hull.
The withdrawals are even more worrying for Van Gaal as Liverpool chase them down for fourth place.
Brendan Rodgers' men face a crunch clash with Chelsea tomorrow afternoon (4pm), knowing a win is vital if they are to return to the Champions League next season.