Kupp will miss at least four games. The move comes after the 30-year-old was ruled out for the team's Sunday opener against the Seattle Seahawks.
Head coach Sean McVay spoke to reporters Wednesday about Kupp's updated status and painted a cloudy picture of what Kupp might be dealing with.
Initially noting that "soft tissue stuff" was the issue, McVay reportedly said Kupp's injury is not consistent with the symptoms of a normal hamstring strain.
He reportedly visited a specialist in Minnesota a day before he was ruled out. McVay didn't provide specifics about the specialist Kupp saw, but noted the team is "opening every avenue" to understand whether the wideout has a soft-tissue injury or even a possible nerve issue, according to The Athletic's Jourdan Rodrigue.
The Super Bowl LVI MVP landed on injured reserve last season when he sustained a high ankle sprain during the Rams' Week 10 loss to the Cardinals in November. Kupp had to have surgery to treat the injury.
He returned to offseason training after recovering from his ankle issue in June. Kupp's comeback was hampered when he injured his hamstring during practice on Aug. 1. He returned to practice at full capacity and had a setback on Aug. 31.
In Kupp's absence, the Rams will turn to the next-best receivers on their 53-man roster.
Their 2020 second-round pick, Van Jefferson, was reported as the Rams' No. 1 receiver when Kupp was ruled out. Young receivers Tutu Atwell and Puka Nacua are the likely No. 2s and No. 3s.
The team's unofficial depth chart currently lists Ben Skowronek as well. The former Notre Dame receiver was selected with the 249th pick in the 2021 NFL Draft.