The Spanish ace reckons his career has stalled under Van Gaal this season and is planning to discuss his future with the Dutchman.
Herrera joined United from Athletic Bilbao for £29m in June 2014 and was hailed as one of the best attacking midfielders in Europe.
But he has made just 32 appearances and become frustrated at his lack of game time at Old Trafford.
Herrera had to wait until the end of August to make his first Premier League start and has found himself in and out of the team ever since.
Starsport understands Herrera is concerned about his role in the team and how he is asked to play when he is picked by Van Gaal.
A source said: "Ander is worried about his lack of progress at
Manchester United under Louis van Gaal.
"He feels like he's lost his identity as a player and doesn't know what his role is anymore.
"His situation appears to be getting worse and he's worried his career is going backwards, so there will have to be a chat with the manager."
Herrera is under contract at Old Trafford until 2018.
He was hoping that joining United would boost his chances of forcing his way into the Spain squad ahead of next summer's European Championships.
But he is still waiting to be called up and now fears he will miss out on the finals in France.
To make matters worse Van Gaal signed fellow midfielders Bastian Schweinsteiger and Morgan Schneiderlin in the summer to make competition for places even harder.
He has started six Premier League games this season, but is currently sidelined with a hamstring injury he suffered in United's recent win at Watford.
News that one of his stars is unhappy is the last thing Van Gaal needs as he faces increased criticism about his tactics.
United are struggling to score goals and have been accused of playing boring football after drawing six of their last nine matches, with home fans booing them off following last week's bore draw against PSV Eindhoven in the Champions League.