The highly-rated midfielder, 25, joined The Blades in 2000 from Manchester City and has become a pivotal figure at Bramall Lane.
United are keen to tie the Hartlepool-born ace to a longer deal to ward off potential suitors.
Crystal Palace had a £1 million offer for the all-action midfielder turned down in January and West Ham have also been credited with an interest in the star, rated in the £3 million bracket by boss Neil Warnock.
Warnock is also looking to extend the contract of 19-year-old midfielder Michael Tonge who has been watched by a host of Premiership clubs.
