Recent form had seen Joe Wildsmith show himself to be one of the best young goalkeepers in the Championship.
However, no stopper is immune from mistakes and Wildsmith had an afternoon to forget against Birmingham City as Sheffield Wednesday lost 3-1 at Hillsborough.
The 22 year-old conceded after eight minutes when some poor communication between he and Frederico Venancio saw David Davis nip in to open the scoring.
But the day got even worse when on 21 minutes Jota's strike from distance slipped through the arms and the legs of Wildsmith to allow the Blues to double their lead.
The visitors would go on to win 3-1, with Wednesday down to nine men after red cards for Marco Matias and Daniel Pudil and Cotterill admitted he felt for Wildsmith.
However, the Blues manager was in no doubt the keeper will bounce back from the error.
"We had a little bit of luck," said Cotterill. "You feel sorry for the young goalkeeper. I've known the young goalkeeper for a long time and he's going to be a good goalkeeper, he's just had one of the best in the league over the last ten years in Keiren Westwood to oust.
"I just said to him to keep his head up because he will become a very. very good young goalkeeper. I know that in time if he stays here long enough he'll be Sheffield Wednesday's number one. He's got a great career ahead of him. I told him not to take that one too hard."
Sheffield Wednesday match report: Owls 1 Birmingham City 3
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