"I felt a cramp," Baez said. "After I passed first base, [my leg] went back to normal. When I stopped, I felt the cramp. Obviously, [manager Joe Maddon] didn't want me to stay in the game. I'm completely fine, 100 percent. I got some treatment. The [athletic] trainers were all over it, and everything is fine."
The Cubs had two runners on and nobody out against the Padres' Jordan Lyles when Baez hit a double into the left-center-field gap in the second. Both runs scored, but Baez limped into second base. Maddon went out to talk to Baez, and the infielder came out of the game.
"It's scary," Cubs pitcher Tyler Chatwood said about seeing Baez leave the game. "The goal for everybody is to get out of here healthy and ready for the season."
"I haven't been drinking a lot of water," Baez said. "I drink water during the workouts, but outside of the workout, it's also important, and I haven't been drinking a lot of water."
He was not scheduled to play on Friday, and could be back in the lineup for one of the Cubs' split-squad games Saturday if he passes all the tests.
"We still have almost three weeks [before the season starts]," Baez said.
Chesny Young, who replaced Baez as a pinch-runner and took over at second base, also had to come out of the game after colliding with first baseman Anthony Rizzo in foul territory chasing Wil Myers' popup in the third inning.
"I didn't see the play but saw somebody crash," Baez said. "I thought, 'No way. It can't be two in one day.'"
Young appeared to be shaken up on the play and was taken out as a precautionary measure.
Baez's double came in a five-run second inning, when the Cubs smacked six straight hits off Lyles.
"A few of the pitchers who came from watching the game, they were talking about our hitting today," Baez said. "Obviously everybody is feeling good. We have a lot of energy in the clubhouse. Since [Yu] Darvish signed, we got everybody together. We're feeling great. I feel the team is as motivated as the [2016 season]."