McCullers (back) completed a three-inning, 45-pitch simulated game Sunday morning, Jake Kaplan of the Houston Chronicle reports.
This is a major step in his recovery from a back injury that has kept him sidelined all month, and if everything is still feeling in order Monday, his next step could be to head out on a minor-league rehab assignment. The Astros haven't determined how many rehab starts he'll need to make before rejoining the big-league rotation, but it will be multiple outings.