The 19-year-old England international joined Stoke on transfer deadline day but has been loaned back to the Championship club for the rest of the season.
Clark, who gave Butland his Blues debut in August, expects the youngster to reach the very top and has praised him for snubbing Chelsea in the final week of the January window.
"We've lost in terms of the long term, in my opinion, the best goalkeeper in Europe," Clark told BBC WM.
|6/4||Birmingham are 6/4 with Bet365 to beat Nottingham Forest at St Andrew's on Saturday|
He added: "I think many young players would have jumped at that [Chelsea] 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.
"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."