According to Paul Sullivan of the Chicago Tribune, Mark Prior "seems headed for the non-tender list" unless the Cubs pull off a trade or Prior concedes to an option year for 2009.
The 27 year-old hasn’t started a big league game since August 10th, 2006. If he becomes a free agent, I imagine many teams would view him as a low-risk, high-reward option. The Padres have cooled on him, though.