"Stephen is in a lovely groove of good form at the moment," Clough told the club's official website.
"In fact, in the last eight months since I have been in charge he has only made a single mistake which was at Doncaster last season.
"Apart from that, Stephen has been exemplary. He is fully fit and probably close to the peak of his career.
"Goalkeepers mature that little bit later than outfield players and that only comes with playing games."