The young Dane has started eight of United's 12 games this season.
But Amorim concedes: "You can feel the anxiety every time Patrick touches the ball. I can feel the anxiety.
"When I see Patrick playing for the national team, he scored a great goal against Scotland and the decision that he made under pressure was completely different than the decision he's making in our team. I think it's the decision, he needs to be calmer playing the game.
"remember the shot against Everton. That was easier than the decision he had to make when a guy from Scotland was there. I saw it when he played in Italy.
"But again, here is different and sometimes the pressure is hard for them in the beginning. He has time to improve."
United meet Crystal Palace at Selhurst Park in today's early kickoff.