Darnold is dealing with a sprained right foot, both Rich Cimini of ESPN.com and Manish Mehta of the New York Daily News report.
According to Mehta, Darnold's sprain is "significant," and the expectation is that quarterback won't be available Sunday against the Bills. The Jets have yet to confirm that will be the case, but those who have been relying on Darnold in fantasy leagues should begin weighing other options. If Darnold is in fact sidelined for Week 10, Josh McCown would draw the team's starting assignment.