SAN FRANCISCO -- Giants reliever Reyes Moronta departed Saturday night's 4-1 loss to the Padres in the sixth inning with an acute right shoulder strain and is scheduled to undergo an MRI exam Sunday to determine the severity of the injury.

Moronta was summoned to relieve starter Logan Webb with a runner on second base and two outs in a 1-1 game, but he immediately fell to the ground after throwing a 2-0 fastball to Luis Urias, prompting team athletic trainer Anthony Reyes and manager Bruce Bochy to rush out from the dugout. Moronta appeared to be in significant pain, lying on the ground for a few minutes before walking off the field with Reyes clutching Moronta’s right arm.

"He went down, so no question, there’s concern," Bochy said. "Especially when you’re calling it an acute right shoulder strain. We just have to wait to see the results from the MRI to see what’s happened here."

Tyler Rogers came in to replace Moronta and walked Urias, but he induced an inning-ending groundout from Austin Hedges to keep the 1-1 tie intact.

Moronta has been a key cog in the Giants' bullpen over the last two seasons and entered Saturday with a 2.86 ERA over 56 2/3 innings. The 26-year-old previously underwent Tommy John surgery in 2013 while pitching for Class A Short-Season Salem-Keizer, but Bochy said the Giants don't believe he's reinjured his right elbow.

"That’s a tough break for Reyes," Bochy said. "He’s one of our guys, and he’s going to be down I’m sure for awhile. I don’t want to speculate what’s going on because we don’t know, but he’s a guy that we’ll miss in that bullpen."

Cueto update

Right-hander Johnny Cueto worked six scoreless innings in his sixth and final rehab start with Triple-A Sacramento on Saturday. Cueto allowed four hits while walking none and striking out six in the 75-pitch effort. Barring any setbacks, the 33-year-old veteran is expected to make his next start for the Giants, completing his long road back from Tommy John surgery.