NFL Network Insider Ian Rapoport reported Sunday night that it appears at first glance Kupp "may miss some time, but [the injury is] not catastrophic," adding that he will still undergo further testing.
Kupp had jumped up to catch a throw from Rams backup quarterback John Wolford, and landed awkwardly, with his right ankle getting rolled up on. Kupp laid on the ground for a few minutes before being helped up, and Kupp hopped to the sideline bench without putting weight on it.
He later was able to make his way to the locker room under his own power, but with a clear limp on the right side. Kupp did not return to the game, and the Rams fell to last place in the NFC West with a 3-6 overall record and a 1-3 mark in the division.
In his post-game press conference, head coach Sean McVay expressed concern for Kupp's injury, saying that while he'll talk with the medical staff later to learn more, initial reports were not positive.
"I don't have anything right now," McVay told reporters. "I just know it didn't look good, it didn't sound good."
Kupp had been the most consistent presence on a Rams offense that's struggled to get things going this season, collecting 100+ receiving yards five times and averaging 101.6 yards per game.
His worst outing of the season by far before this week was in the Rams' first game against the Cardinals, when he hauled in four catches for 44 yards. But those numbers were nothing compared to the struggles on Sunday, as Kupp finished with three catches on five targets for -1 yards before the injury, the first time in his career he's finished with negative receiving yardage. While Kupp played without his starting quarterback Matthew Stafford, who's still in concussion protocol, this was still a significant drop in production in comparison with his teammates.
In past games when things have gotten tough, Kupp has been there to keep the Rams offense moving, but if his ankle injury is severe, as McVay indicated, the Rams will need to find a way to play without their star.
Los Angeles will next visit the similarly struggling New Orleans Saints next Sunday.