Donald returned to the sideline but did not re-enter the game. The Rams beat the Seahawks 30-20.
Rams coach Sean McVay did not have an update on Donald's injury immediately following the game, telling reporters, "I will have more information for you later on."
Donald landed a quarterback hit on Russell Wilson as the Seahawks' QB hurried a deep pass that fell incomplete. But Wilson appeared to land on Donald's ribs on the tackle. Donald clutched his abdomen as he rose to his feet, and before leaving the playing field took a knee in apparent pain.
Donald had sacked Wilson twice before leaving the game.
A two-time NFL Defensive Player of the Year, Donald finished the regular season with 13.5 sacks for the top-ranked Rams defense.
Rams receiver Cooper Kupp also limped off, grabbing his right knee in the closing minutes of Saturday's win. McVay did not have an update on Kupp's injury.