On Wednesday, coach Sean McVay said wide receiver Cooper Kupp, who was placed on the reserve/COVID-19 list on Tuesday, is unlikely to play Sunday.
Kupp, the team's leading receiver with 974 yards, must remain on the list for 10 days if he tested positive or five days if he is considered a high-risk close contact of someone who did. If Kupp is not considered a high-risk contact then there is no stringent timetable attached to his return.
The team did not disclose whether he tested positive or was deemed a close contact to someone who did.
Meanwhile on Tuesday, the Rams officially signed quarterback Blake Bortles from the Denver Broncos' practice squad in a move McVay said to expect after announcing Monday that quarterback Jared Goff will not play against the Cardinals after undergoing thumb surgery.
Quarterback John Wolford is slated make his first NFL start in Goff's absence. Bortles, who is familiar with the Rams' offense after serving as Goff's backup last season, will back up Wolford.
Along with a quarterback who has never appeared in an NFL game and uncertainty at the wide receiver position, the Rams also will be short-handed in the backfield against the Cardinals.
Rookie running back Cam Akers also is dealing with a high ankle sprain he suffered in Week 15 and caused him to be inactive against the Seahawks. McVay said Monday there's a possibility that Akers will be available on Sunday.
However, because of the typical four-to-six-week recovery for most high ankle sprains, it remains most likely that veteran running back Malcolm Brown will start and bear most of the workload, with rookies Xavier Jones and Raymond Calais backing him up.
Jefferson has caught 15 passes for 170 yards and a touchdown this season.
The Rams have won seven straight against the Cardinals under McVay.