Jansen (oblique) began a rehab assignment with Single-A Dunedin on Tuesday, Keegan Matheson of MLB.com reports.
Jansen hasn't played in a full month while recovering from a strained left oblique. The length of his absence may mean he needs more than just a game or two of rehab before he's ready to return, though the Blue Jays haven't specified exactly how much time he'll need.