Wynns (shoulder) will begin a rehab assignment with Triple-A Louisville on Sept. 17, MLB.com reports.
Wynns suffered a right teres major tear but was recently cleared to throw to bases. He is on the 60-day injured list and not eligible to return until Sept. 27, two days before the end of the season. While it's possible he could make a late-season return, it wouldn't seem to be a given that he's added to the Reds' roster.