SAN FRANCISCO -- San Francisco Giants right-hander Reyes Moronta will undergo an MRI on his throwing shoulder after leaving Saturday night's 4-1 loss to the San Diego Padres.

Manager Bruce Bochy said after the game that Moronta suffered an acute shoulder strain.

Moronta fell off the mound and writhed on the grass after throwing a 98-mph fastball to Luis Urias on his third pitch. The reliever delivered a swinging strike, but recoiled with a yell before dropping to the ground. He held his right arm gingerly as he walked off with the help of a trainer.

The 26-year-old came into the game in relief of rookie Logan Webb with two outs in the sixth inning.

"There's no question there's concern. We have to wait for the [MRI] results though,'' Bochy said. "It's a tough break for Reyes. He's one of our guys and I'm sure he's going to be down for a while.''

Moronta was 3-7 with a 2.86 ERA in 55 relief appearances entering Saturday. The second-year player has 70 strikeouts in 56⅔ innings.

Information from The Associated Press was used in this report.