The Blades paid £1.85m to Swedish club Helsingborgs for his transfer last year after his record of nine goals in 19 appearances caught their attention, and they will be looking to recoup most of that if they sell him on.
The 22-year-old was signed in January 2007 by former boss Neil Warnock, but he has started just seven league matches and featured on only three occasions under current boss Kevin Blackwell.
Blackwell has a number of strikers available to him, including James Beattie and Rob Hulse, and Shelton may find his opportunities limited again next season.
Shelton has two years remaining on his current deal and the youngster is believed to be interesting a number of other clubs.
Leeds would have to secure a work permit for the forward if they sign him on a permanent basis.
Shelton netted twice in Jamaica's 7-0 victory over the Bahamas in a World Cup qualifier on Sunday and he has scored four goals in 10 starts for Sheffield United with 15 sub appearances.