The Dane has been superb in his first months as a Premier League player.
Cooper told Viaplay: "There is no doubt that Mads has had a good start to the season. He is a talented, young goalkeeper with some strong qualities."
But according to Cooper, the Dane's development does not stop here.
"This is only the beginning. He must - and he does - aim to improve even more and aim to play at least at the same level and maybe even better.
"We are only seven games in, but it has undoubtedly been a good start and we like his attitude and the person he is."
Cooper was also asked about Denmark defender Jannick Vestergaard.
He added, "No player is guaranteed to be selected. It's not the right culture, I think.
"Whether it's Jannik or the midfielders. I get asked about them a lot. If they play and such.
"What I know, I have, it's good headaches in relation to decisions about who will play.
"As long as they push each other to training and give their best, then these are the decisions you want to make, even if they are hard to make.
"Because you know that everyone is ready to play. Jannik is preparing properly and when he plays again, I am sure he will be more than ready to deliver the performance we all want."