The Dutch winger was heavily criticised by Arsenal manager Arsene Wenger in the previous round for perceived play-acting, and Moyes, while refusing to name players individually, has said that the referees must be wary of simulation.
He told reporters: "We trust the referees to make the right decisions. Diving is one of the hardest things for referees to get right.
"I would have retrospective cards but I wouldn't want to comment on individual players."
The second leg of the quarter-final tie will be played on April 9.