The 24-year-old frontman has recovered from his injury problems and played a key role in the Blades fine start to the season, scoring nine goals so far.
He has, however, rejected the offer of a new contract and may be sold in January to prevent him leaving on a free transfer next summer.
Kevin Blackwell knows the player from his time at Bramall Lane and could be lining up a surprise bid if today's stories are accurate.