The Cubs said he will report to their minor league facility in Mesa, Ariz., by Sunday and work with pitching coordinator Mark Riggins.
Their hope is that he will be a good addition to their bullpen by season's end.
"He's not ready (now)," Assistant General Manager Randy Bush said on Chicago's Web site. "(But) What's great is that he wants to do it the right way."
Toronto signed him to a five-year contract, $47 million, before the 2006 season after six in Baltimore, but he missed 2007 because of "Tommy John" reconstructive left elbow surgery.
Ryan, 33, was erratic in 25 relief appearances (20 2/3 innings) this season when the Blue Jays released him on July 8.
He had been replaced in the closer's role by Scott Downs.