The Rams elevated Witherspoon from the practice squad to the active roster Saturday.
Witherspoon signed with the Rams' practice squad Wednesday.
Witherspoon is slated to sign with the Rams on Wednesday, Jordan Schultz of BleacherReport.com reports.
Witherspoon logged seven total tackles (four solo), including one tackle for loss while also deflecting a pass in Sunday's 26-25 win over the Giants.
Witherspoon (groin) does not carry an injury designation into Thursday's game versus the Saints, Adam Caplan of SiriusXM NFL Radio reports.
Witherspoon (groin) was estimated as a full participant at the Rams' walkthrough practice Tuesday, Adam Caplan of SiriusXM NFL Radio reports.
Coach Sean McVay said Monday that he expects Witherspoon (groin) to play Thursday versus the Saints, Gary Klein of the Los Angeles Times reports.
Witherspoon (general soreness) returned to Sunday's game against the Eagles, Jourdan Rodrigue of The Athletic reports.
Witherspoon is considered questionable to return to Sunday's game against the Eagles with cramping, Adam Grosbard of The Orange County Register reports.
The Steelers informed Witherspoon (hamstring) on Wednesday that he will be released, Ian Rapoport of NFL Network reports.