Engel suffered his setback in his recovery from a hamstring strain and is at least three weeks away from beginning a rehab assignment, Scott Merkin of MLB.com reports.
It's a poorly-timed setback for the White Sox, as Luis Robert was ruled out for most of the season with a strained hip flexor Monday. Engel could be the primary center fielder once he's ready to go, but that won't happen until the last few days of May at the earliest.