The 22 year old is also to said to be chased by Championship new-comers Reading. Paddy Kenny is still to be Blackwell's first choice but Gerken may be bought to provide back up to the Irish goalkeeper.
2nd choice keeper Ian Bennett's contract is up but it is not known whether he is to sign a new deal at the Lane or not. Moving more down the pecking order, Paul Gerrard the 3rd choice shot stopper has been told his contract with United is over.
£500,000 is the fee said to be paid by the Blades. There has also been rumours that Luton Town number one Dean Brill may join the South Yorkshire outfit.