The Spireites are looking for a new manager following the decision not to renew Lee Richardson's contract after failure to reach the League Two play-offs for a second successive season.
Former Nottingham Forest boss Calderwood, 44, is on a shortlist of candidates, with Chesterfield set hopeful of making an appointment next week.
"Colin Calderwood has applied. Yes, we have spoken to him. But there are three (on the shortlist), which if any one of them came I'd be delighted," Hubbard told BBC Radio Sheffield.