Schefter spoke to a source who said the Rams believe Kupp "could miss some time" but don't have a specific time frame for how long they could be without the second-year pass-catcher.
A sprained MCL isn't the best-case scenario for Kupp and the Rams, but things seemingly could've been worse considering how the injury happened.
During the second quarter of Sunday's game, Broncos safety Darian Stewart brought Kupp down with a horse-collar tackle. Kupp's left leg bent awkwardly on his way to the ground and he was carted off the field.
Kupp returned to the game, but he didn't register a reception in the victory.
The 25-year-old has caught 30 passes for 438 yards and a team-high five touchdowns through six games, and he sits seventh among qualified receivers in DYAR (defense-adjusted yards above replacement) on Football Outsiders.
The Rams still have Robert Woods and Brandin Cooks, the latter of whom is seventh in the NFL in yards per reception (18.0), while Todd Gurley is averaging a league-best 103.8 yards per game on the ground.
While Kupp is a vital member of the offense, the Rams still have a bevy of talented skill position players to help pick up the slack until he returns.