Schwarzer has warned the former Atletico Madrid man that the Premier League is a far tougher training ground than La Liga.
He told talkSPORT: “That’s the downside of playing for a club like Man United.
“He’s going to have to find his form very, very quickly. It’s going to be a very, very tough school for him.
“The Premier League and Spanish leagues are worlds apart in the type of football that is played.”