The frontman has netted seven times for Northampton since moving from Sheffield United in August and returns to Bramall Lane 'a better player' according to Wilder.
"We move on," the Town boss told the club's official website.
"We are looking to improve the group and we are confident that we can do that."
Midfielder Ryan Watson has also left Sixfields, returning to Leicester City, as Wilder prepares the ground for January transfer window signings.
In terms of new arrivals, Wilder has some breathing space as his side are in FA Cup action this Saturday although the game against MK Dons is set to be fiercely contested in front of a big crowd.
Update: The new man is already in the building with James Collins signed on loan from Shrewsbury until the rest of the season, the 25-year-old being allowed to leave the League One club despite being a regular starter.
As of Monday only a handful of tickets remained for the visit of the Championship side.