Birmingham boss Lee Clark believes Jack Butland could become Europe's best keeper following his move to Stoke.
England international Butland, 19, made a move to the Potters on deadline day, but has returned to Blues on loan for the rest of the season.
"We've lost in terms of the long term, in my opinion, the best goalkeeper in Europe," Clark told BBC WM.
"We've got him back for the rest of the season, but I would just love a bit more time to work with him."
Butland was heavily linked with a move away from the financially stricken Championship side throughout the January transfer window.
One of the clubs that were interested in Butland was Chelsea, but the keeper instead opted to sign a four-and-a-half-year contract at the Britannia Stadium - worth a potential £3.5m for Blues - where he felt first-team football was more likely.
"I thought it was unbelievable maturity from the boy not to pursue that one [Chelsea] because in the short term he didn't see a route into the first team," Clark said.
"That's unbelievable. I think many young players would have jumped at that for the profile and financial rewards.
"But Jack looks at the bigger picture. He's not only a top player but he's a top young guy.
"It's easy to be a top player, but what he's shown over this transfer window is that he's unbelievably mature and got a great awareness of what life's about."
And Clark added: "He knows eventually he's going to be at a top club, and that's not disrespectful to Stoke who are a great Premier League club and have a fantastic manager, but ultimately he's going to end up at a Champions League club competing for the higher honours."