Diaz (oblique) is starting a minor-league rehab assignment Tuesday, Chandler Rome of The Athletic reports.
The 27-year-old has been on the injured list since early May due to an oblique strain, but he's been cleared for game action after ramping up his baseball activities. Diaz had a poor start to the season offensively with a .602 OPS through 26 games, and Christian Vazquez's superior work behind the plate could mean that the Astros deploy a more even split of playing time at catcher, per Rome.