The Cardinals activated Lynn (knee) from the 15-day injured list Wednesday.
Lynn will rejoin the rotation Wednesday versus the Reds after missing the last six weeks of action with right knee inflammation. He made one rehab start, allowing five runs over 3.2 innings while throwing 80 pitches for Triple-A Memphis on Sept. 1. The last couple spots in the St. Louis rotation are in flux, so Lynn likely will need to pitch well in order to continue being given additional starts down the stretch.