The deal should go through tomorrow at the very least if everything goes to plan. Henderson bagged 13 goals for the Hornets in the last campaign and is set to put pen to paper at Bramall Lane.
Rumours are spreading around that James Beattie could be out for two to three months but will Henderson easily slide into the starting XI and is £2.25m worth it despite having Billy Sharp and Jon Stead on the striking books.
Meanwhile Luton Shelton is on the brink of signing for Valerenga of Norway.