Castro was running to first base after hitting a ground ball in the fourth inning when he grabbed his leg while running down the first-base line.
"The hammy is a little tight," Castro said after working with the team's medical staff. "I don't think it will be too bad. When I got to first base I felt it when I touched the base. After I came out I stretched and ran a little bit. Let's see (Thursday) how I feel and what the trainer tells me. I think it is going to be (alright)."
Castro, an All-Star the past two seasons who played all 162 games for the Cubs last season, was the team's DH on Wednesday and was batting for the third time in the game.
"I told (manager Dale Sveum) I wanted three at-bats today," Castro said. "Next time I will only ask for two."
Castro, who said he has never had any leg issues during his career, signed a seven-year, $60 million contract with the Cubs last summer.