Gregerson, who has missed 24 games with a right oblique strain, made his second Minor League rehabilitation assignment Sunday with Triple-A Tucson, which was playing in Sacramento.
Gregerson struck out two in one scoreless inning, though the results of his two outings with Tucson weren't something that concerned manager Bud Black.
"He felt good. The thing that's important is the physical," Black said.
Gregerson allowed three runs on three hits and two walks while getting one out Friday while pitching for Tucson.
Black said the Padres would either reinstate Gregerson from the disabled list after the game Monday against the Giants or before Tuesday's game. There's a small chance Gregerson will need another rehab appearance, Black said.
Gregerson was placed on the disabled list June 9, retroactive to June 7.
He first felt some pain in his left side while warming up in the bullpen in a game on June 8 against the Rockies and immediately stopped.
At the time of the injury, Gregerson was 2-1 with a 2.63 ERA in 30 games.