Soto started during Sunday's 7-5 loss against the Reds and doubled in the eighth inning, sliding head first into second base. He stayed in the game but Cubs manager Mike Quade said the catcher woke up on Monday with some pain. Soto underwent the MRI at Northwestern Memorial Hospital.
Soto said he was able to play with his kids Sunday night and felt a little discomfort. He wanted to have the MRI to make sure there was nothing seriously wrong.
"I have a little bit of fluid that prevents me from straightening it out," Soto said. "It's fine, I'm day-to-day, and hopefully I'll be better tomorrow or the next day."
Teams can expand their rosters on Wednesday, so the Cubs will likely add another catcher at that time. Koyie Hill started on Monday.
Soto was activated from the disabled list one week ago after being sidelined with a sprained ligament in his right shoulder. He batted .250 on the six-game road trip.