The 31-year-old made his name at Blackpool, scoring 45 goals in only 105 starts for the Seasiders.
However, Ormerod's career has stalled since he moved to Southampton for £1.75million almost seven years ago.
He found the net only 12 times in over five years with the Saints and was loaned out to Leeds United and Wigan Athletic during his spell on the south coast.
Preston snapped him up on a free transfer in January 2006 but the Blackburn-born forward has failed to establish himself as a first-team regular at Deepdale.
He has scored only 13 goals in 62 league appearances for the Championship side and ended last term on loan with Nottingham Forest.