"He's just got cramps, his legs are a little sore," said manager Ozzie Guillen. "He wasn't going to play today no matter what."
Buck was removed in the ninth inning of Wednesday's 15-5 loss after his legs and back cramped.
After he homered over the Green Monster in the seventh inning, Buck felt discomfort in his back. He said he drank two Pedialytes before the game to battle dehydration on a humid day, but still cramped late in the contest.
"If I didn't have that I would have cramped in the fourth inning," Buck said on Thursday. "I feel good now."
Brett Hayes started in Buck's place and hit ninth in Guillen's lineup.