The Cardinals activated Robertson (elbow) from the 15-day injured list and optioned him to Triple-A Memphis on Monday.
Robertson has moved past the right elbow injury that sent him to the IL a month ago, but he'll remain at Memphis, where he had been on a rehab assignment. The right-hander holds a 4.38 ERA and 14:2 K:BB over 12.1 innings during his time in the majors this season.