Initially, the Cubs said Castro would be out of the lineup for seven to 10 days, but on Friday morning, manager Rick Renteria gave no exact timetable on when Castro might play again.
"I don't have a set date in my head right now," Renteria said. "That's all based on how he's progressing. He's progressing well."
Earlier in the week, Castro indicated he might be back by this weekend, but Renteria said he wouldn't play before Monday. Now, Castro says it could be another week, as he's running at only "40 percent."
"I don't want to rush myself," Castro said. "If I can play in 10-12 games in spring training I think I'll be good for the season."
The Cubs have 16 days of games left on their spring schedule before their season opener in Pittsburgh.
"He knows his body more than I do," Renteria said. "He could be 75-80 percent in 3-4 days. We just don't know."
Castro injured his right hamstring sliding into second base during the Cubs' second Cactus League game. He hurt his left hamstring last spring and went on to have the worst season of his career, although the injury didn't plague him during the season. He started taking batting practice Thursday.
He wants to be 100 percent come April and wants to get back to stealing bases again. He had just nine last season after swiping 25 in 2012.
"That's one of my goals," Castro said. "Steal a lot of bases. I can do it because I have a green light now. When I want to run, I run."