Soto has been out since straining his right groin on July 21. Soto was in the lineup for Friday night's game against Houston.
He's played just three games this year after missing the first part of the season following surgery to repair torn cartilage in his right knee in March. Soto hit .375 in five rehabilitation games at Triple-A Round Rock.
Williams was 1-1 with a 9.90 ERA in two starts for the Rangers this season. The Rangers have 10 days to trade, release or outright Williams to the minors. It is the second time he's been released this season after the Astros designated him for assignment on June 30.