Riggott, 30, is a free agent after being released by Middlesbrough in the summer.
James Coppinger has signed a contract extension with Doncaster Rovers, keeping him at the Keepmoat Stadium until 2013.
Coppinger has been with the Yorkshire side since 2004, when he moved from Exeter City.
Queens Park Rangers have given a new deal to defender Kaspar Gorkss, who is now also tied to Loftus Road until 2013.