De Gea started on the bench after the Dane was outstanding a midweek run-out at Under-21 level although the manager admits the Spaniard will return for the visit of Wigan in the next Barclays Premier League outing.
"I think young David made a mistake last week [against Fulham]," he told Sky Sports. "He knows it. With the form he's been in, he's been making some fantastic saves, but one error like that could have cost us the game.
"It's just a learning process for him and he'll be back in a couple of weeks' time."