McCallum penned a four-year deal at Bramall Lane, arriving in South Yorkshire on a free transfer following the expiration of his contract at Norwich City, where last season he was part of the Canaries squad that made the Championship play-offs.

The Kent born operator spent time in Jamie Vardy's V9 Academy before being snapped up by Coventry City in August 2018.

Norwich paid £3.5 million for his services, and he has developed ion the EFL with a loan spell back at the Ricoh Arena and more recently QPR.