Millwall informed the Blades that their centre-back is not for sale.
Title favourites Blades travel to The Macron with high hopes, but Bolton are equally hopeful of a return to the Championship.
Everton have been heavily linked with a move for Sheffield United striker Dominic Calvert-Lewin.
English League Two Champions Northampton Town have granted Charlton Athletic permission to approach manager Chris Wilder and assistant Alan Knill.
HITC Sport understands that the Cobblers boss is in the frame to succeed Dean Saunders at the Proact Stadium.
HITC Sport understands Northampton Town boss Chris Wilder is a contender for the vacant York City job.
Barnsley are rooted to the foot of the Championship table, and their poor showings this season have cost manager David Flitcroft his job at Oakwell.