Mateo signed a major-league contract with the Rays on Wednesday, Francys Romero of BeisbolFR.com reports.
Mateo was cut by Atlanta over the weekend after clearing waivers, but he'll now receive a new opportunity to carve out a role for himself with the Rays. The 31-year-old has slashed .240/.285/.380 across 137 plate appearances this season and figures to bolster the team's infield depth while Ben Williamson (hamstring) is on the injured list.