Diaz agreed to a minor-league contract with the Padres on Monday, Daniel Alvarez-Montes of ElExtraBase.com reports.
Diaz was let go by the Rockies on Aug. 16 after hitting .196 with eight RBI and five runs scored in 28 games since July 1. He'll get a chance to start fresh in San Diego, where he figures to serve as depth behind the dish at Triple-A El Paso.