Washington (quadriceps) didn't participate in Thursday's practice, Tim Twentyman of the Lions' official site reports.
The Lions haven't officially ruled Washington out for Sunday's game against the Falcons, but his failure to practice the last two days makes it unlikely that he'll be able to rally in time to dress in Week 3. If that's the case, Zach Zenner would likely be active for the first time this season as the Lions' No. 3 running back, with most of his offensive snaps coming in short-yardage scenarios in the red zone.