Ahead of their trip to Europa Conference League opponents Astana, Maresca was asked if Palmer was the best player in the Premier League.
"He could be in this moment," the manager replied. "But in England, they are quite lucky because in the Premier League, there are so many good players. For sure, Cole is one of them but it is full of fantastic players, the Premier League."
Asked about Palmer becoming world class, Maresca also said: "Absolutely, he can be.
"But he is just 21 so he can do many, many things better. He has to learn many things. He has to learn - and is learning in this moment - that everyone is marking him man-to-man, but there are many things he can improve, for sure."
- Get breaking football news faster with the new Tribal Football app! Download now on iOS and Android to stay ahead of all the latest transfers and football updates. Download now: App Store, Google Play