Herrera came on as a second-half substitute in matches against Tottenham and Aston Villa, and the United manager might have risked angering the Spaniard by revealing he could be left out again for the coming games.
Van Gaal opted to play youngster Adnan Januzaj and, when questioned about his decision, he said: "Because he gave signals in training that he is more and more confident, but also better.
"I like a second striker in that position (behind Wayne Rooney) more than a third midfielder. That is why, for example, Herrera is not playing but is always coming on as a substitute, because he is more of a controlling midfielder there."
GETTY
Ander Herrera came off the bench against Tottenham and Aston Villa
The United boss was rewarded with a goal from his young charge and could opt to leave Herrera, 26, on the bench for Tuesday's Champions League play-off with Club Brugges.
Competition at Old Trafford is fierce in midfield, after the additions of Morgan Schneiderlin and Bastian Schweinsteiger.
They have also been linked with a move for Lazio's midfield enforcer Lucas Biglia.
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