The 21-year-old was a member of England Under-17s World Cup-winning squad in 2017, when they beat Spain 5-2 in the final.
“Curtis will be the best goalkeeper in this league,” said Fell.
“He just oozes class and quality. There was nothing he could do for the goal on Tuesday night but everything he did was fantastic.
“Signing him is a real coup for us. I don’t know whether we will be able to keep hold of him until after this season.
“But if we can help him and he can help us by getting us up the table this season, then you never know what might happen.”
Fell also had warm words for young striker Joe Rodwell-Grant, who has arrived on loan from PNE, and has featured in the past two games.
“He was excellent on Saturday and was good again on Tuesday,” said Fell. “He just needs a goal to set him off.”