Righty Nick Vincent, who pitched 1 1/3 innings of scoreless relief in Saturday night's game, was optioned to Tucson to make room for Stults.
"We felt as though we needed some length out of our bullpen. With Stultsy, he gives us that," Padres manager Bud Black said. "The bullpen's been a little taxed the past couple days. He's a fresh arm to help us in the next day or two."
Stults had been on the DL retroactive to June 4 with a strain of his left lat. Prior to the injury, the 32-year-old was 1-2 with a 3.33 ERA in four starts with San Diego.
Stults threw 6 2/3 innings over the course of two rehab starts with Tucson, and was scheduled for another rehab start this weekend. But despite the fact that his rehab has been, presumably, cut short, Black said the Padres are confident he is physically ready to pitch Sunday, if needed.
"He's full strength, Black said. "He threw here in front of us in a simulated game situation, made two Minor League starts where his pitch count got up to 75 pitches. Our reports we got from his last start were very solid."