The Robins have struck a deal with Brisrtol City for striker Christian Roberts worth to be around £50,000 fueling speculation linking Parkin with the Blades.
Sam Parkin: On way out of County Ground?
Parkin joined the County Ground Club from Chelsea in August 2002 and on his debut at home to Barnsley netted a hat-trick in a 3-1 win.
The six foot four striker had previously being on loan at Millwall, Wycombe, Oldham Athletic and Northampton prior to his transfer to Swindon.
It is believed that the Blades will pay £50,000 to take Parkin to Bramall Lane in a deal that's looks already done as the robins find an replacement.