Steele (hamstring) was activated from the 10-day injured list Thursday and optioned to Triple-A Iowa, Jordan Bastian of MLB.com reports.
The left-hander has been on a rehab assignment with Iowa over the past couple weeks, and he'll remain with the minor-league club now that he's healthy. It's likely a temporary stay in the minors for Steele, who has a 2.03 ERA, 1.05 WHIP and 21:7 K:BB across 13.1 innings for the Cubs this year.