The 23-year-old Irishman has struggled to stay in the first-team frame under manager Simon Grayson and spent most of last season on loan at Oldham and then Swindon.
Sheehan was a regular for Swindon, making a total of 26 appearances, and helped them reach the npower League One play-off final.
He initially arrived at Leeds on loan from Leicester City in January 2008 before signing a permanent deal the following summer for an undisclosed fee.
Source: PA
Source: PA