After the 27-20 win, coach Jay Gruden said Kelly possibly has a fractured rib, according to ESPN's John Keim.
Kelley had 78 yards on 12 carries before exiting.
Kelley signed with the Redskins last year after going undrafted out of Tulane. Although he didn't initially get much playing time as a rookie, he earned a more extensive look around midseason and responded by showcasing a powerful running style en route to 704 rushing yards and six touchdowns on the ground.
The 24-year-old New Orleans native has remained mostly durable despite his willingness to run between the tackles. He missed just one game across the four years he was active with the Green Wave. He did suffer a knee injury late last year before undergoing offseason surgery on the ailment.
If he's forced to make a rare stay on the sideline, Washington will likely turn to Chris Thompson to lead the rushing attack. It could also lead to an uptick in playing time for Samaje Perine and Mack Brown as part of the team's backfield rotation.
All told, the timing of the injury is unfortunate for Kelley, who's been receiving an opportunity to prove he could become a crucial cog in the team's offensive attack. Exactly where he slots back in once healthy depends on how the other backs perform in the meantime.