Lee was pulled after the seventh inning of the Cubs' 5-3 win over the Reds. He re-aggravated a bulging disc in his neck in the sixth when he slid into second base.
"You've got to slide," Lee said. "I don't know what to do, honestly -- [I have to] slide differently so I don't have to keep coming out."
Somehow Lee survived a belly flop onto the dirt chasing Edwin Encarnacion's foul ball in the sixth. When Lee slides, he hits the ground and it jars his spine.
"I was fine until that last slide," the 6-foot-5 first baseman said.
Lee hit a RBI triple in the Cubs' three-run first inning against the Reds, and he also singled in the sixth.
"It's just one of those unfortunate things where certain things cause it," Lee said. "It's an injury where I can't move. I have to try to avoid those things as much as possible."
Lee received treatment immediately after leaving the game and said he may play Sunday.
"I'm learning my lesson," he said. "It's something I have to be careful with and can't really fight through."
On July 11, Lee was pulled after the sixth because of problems with his neck. He also had to come out of a game April 26 against the Cardinals because of neck spasms, and he subsequently missed two games. He was sidelined another five games in early May. An MRI exam revealed he had a bulging disc.
The Cubs don't need any more injuries. They put Ted Lilly on the disabled list Saturday, and have put 13 players on the DL this year.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.