United take on Millwall at the Den on Saturday in what will be the two sides' first meeting since their promotion back to the Championship this year.
And Wallace will be looking to add to his tally of three goals and one assist for the Lions this campaign.
The 23-year-old signed for Millwall on a permanent basis from Wolverhampton Wanderers in July, having previously starred for Neil Harris' team in multiple loan spells.
But Wallace would have been a Sheffield United player had Wilder had his own way - although the Yorkshireman did not reveal any further details, such as the timing of his side's interest or how close they came to signing him.
United previously raided Wolves for Wallace's former teammate Ethan Ebanks-Landell, however the defender returned to Molineux at the end of his loan spell in May.
Would Wallace have been a good signing for Sheffield United?