The Rays placed Walls on the 10-day injured list Tuesday with a right hip flexor strain, Ryan Bass of Rays.tv reports.
Walls didn't play in his team's last game Sunday, so it seems he's been dealing with the injury for a few days. He'll be eligible to return Sept. 18, but it's unclear whether Walls has a chance to be ready on that date. Jorge Mateo will likely handle the bulk of the reps at shortstop while Walls is shelved.