Williamson (shoulder) will make a sixth rehab start Thursday for Triple-A Louisville, MLB.com reports.
Williamson had a couple of short outings during his rehab, including a rain-shortened outing, which suppressed the buildup of his pitch count and likely led to a sixth rehab start. The left-hander sports a 5.11 ERA and 1.62 WHIP over 12.1 rehab innings.