The Spaniard suffered a groin injury in training and missed the 1-1 draw with Liverpool at Old Trafford on Thursday night.
Van Gaal has revealed Herrera trained as normal on Wednesday in the build-up to the game but was left out after picking up a knock and is now unsure on whether Herrera will feature in the derby at the Etihad stadium.
When asked about Herrera, van Gaal said: “I don’t know. Wednesday he trained with me and he was not injured.”
I really think we missed Herrera against Liverpool on Saturday night. We had a distinct lack of cohesion and fluidity in midfield which is exactly the sort of thing Herrera helps to improve with his particular playing style. In his absence, Michael Carrick and Marouane Fellaini looked desperately pedestrian.
With his fitness in question, I’d be surprised to see Herrera start against Manchester City and I feel that places an even bigger emphasis on Morgan Schneiderlin returning to the starting XI.
However, van Gaal showed against Liverpool that his preference unbelievably is Fellaini and Carrick in midfield, so I do worry about how Man City could dominate the middle of the park without Schneiderlin and Herrera starting. If that happens, United might have no chance.