Heuer (elbow) is on track for another rehab outing this week with Triple-A Iowa, Tim Stebbins of MLB.com reports.
Heuer has struggled mightily on the farm so far, yielding seven earned runs on six hits and six walks through 4.2 innings. He's on the 60-day IL, so the Cubs can slow play the final steps of his recovery from Tommy John surgery until they see better results. There's no exact timetable for his activation.