United have won their last four matches in all competitions despite having as many as 14 players unavailable including captain Wayne Rooney, midfielder Fellaini and defenders Chris Smalling, Luke Shaw, Jones and Valencia.
"Players are coming back but then, normally, they cannot play a match because the rhythm of the game is much higher," Van Gaal told MUTV on Friday.
"Maybe because I'm forced because of the circumstances to take a risk, like I have done with (defender) Marcos Rojo but, when I'm not forced to, then I shall not do that."
The pressure on Van Gaal is lifting following wins over Shrewsbury Town in the FA Cup, Midtjylland in the Europa League and Arsenal and Watford in the Premier League.
Striker Marcus Rashford, 18, scored two goals against both Midtjylland and Arsenal, prompting calls for England manager Roy Hodgson to consider him for the European Championship in France in June.
"It is never too early. As I have said before, age is not important," Van Gaal said. "Maybe you remember me saying this before? Age is not important, it is quality."
United are fifth in the league, level on points with fourth-placed Manchester City and 10 adrift of leaders Leicester City with 10 games left.
"I think everybody wants to win but they cannot always win -- that is the strength of the Premier League," Van Gaal said.
"This is also why the league is popular in the world."
United play arch-rivals Liverpool in the Europa League last 16 and West Ham United in the FA Cup quarter-finals after the trip to 13th-placed West Brom who drew 2-2 at Leicester on Tuesday.
"We have to be prudent and we have to be humble. We have to go now to West Brom, who drew with the leaders in the table, so it won't be easy," said midfielder Ander Herrera.
"But when you are Man United you have to learn to win these kind of games."
(Reporting by Ed Osmond; Editing by Tony Jimenez)
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