Steele (back) was placed on the restricted list Monday, Maddie Lee of the Chicago Sun-Times reports.
Steele experienced low-back tightness during Friday's start against the Brewers, and he'll be unavailable for the Cubs' three-game series in Toronto this week since he's unvaccinated. If his back injury doesn't prevent him from pitching, the southpaw will likely return to action sometime this weekend in St. Louis.