Walls (back) will start at shortstop and bat ninth Sunday against the Mariners, Ryan Bass of Rays.tv reports.
The 30-year-old was withheld from the starting nine in Saturday's 3-2 win due to lower-back tightness, but he'll rejoin the lineup for the series finale in Seattle. Walls is batting .103 (3-for-29) with four walks, three steals and 11 strikeouts in his past 12 games.