The defender carried on from his debut in the Champions League win at Dynamo Kiev last week.
"I've told him he had a good game, but he lost two balls he shouldn't have and I told him. A bad touch can be a chance for the opposition," said Koeman.
"You can have a good game but two errors can cost you the game. He has to learn and improve."
Mingueza's partner at the back, Clement Lenglet, had to go off injured but the coach has reported that the extent of the injury does not appear too serious, although he may miss the midweek trip to Ferencvaros.
"I've spoken to the doctor and it seems like, although we'll need to wait until tomorrow, it's not too serious," said Koeman.
"I don't know if he'll make the game on Wednesday. I hope it's not serious."
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