Soto did take batting practice on Friday and decided to get his hand checked because it felt stiff. X-rays revealed joint irritation.
"I didn't want to push it, because I didn't know what was going on," Soto said. "Everything's fine. There was a little bit of swelling. It's a minor thing."
Soto was one of the heroes on Thursday, when he hit a game-tying three-run homer with two outs in the ninth inning of the Cubs' victory over the Milwaukee Brewers. He apparently hurt his hand during his second at-bat in the fifth.
The rookie flew out to right in the second inning on Thursday, struck out in the fifth, flew out to right in the eighth and then homered in the ninth, hitting his 23rd.
"I felt it in my second at-bat," Soto said. "I took a swing and it felt funny. My last at-bat, I hit a popup to center field and [my hand] didn't pop, but it didn't feel normal. I kept playing, there was adrenaline. When I got home, it got a little stiff and I told the trainers. Hopefully, I'm out there tomorrow."
He is two home runs shy of tying the franchise rookie record for home runs, set by Billy Williams in 1961.
"I hope he gets it," Williams said of Soto. "I hope it's a big home run."
A leading candidate for NL Rookie of the Year, Soto is batting .285 with 86 RBIs.
"To see Geo kind of transform over the years, it makes you happy and almost proud to say you were there in the beginning to see him grow and become the player he is," Cubs shortstop Ryan Theriot said. "Obviously, his ability speaks for itself, but the way he handles himself as a person, he's really turned into a great ballplayer, but more important, a great person."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.