"It's just a little bit tight in the groin," Castro said. "I felt it three days ago when we played the night game, and just a little bit. I don't want to take a chance -- we have two weeks left. I don't want to take a chance and rush myself and get hurt."
The Cubs have Monday off, and they return to Cactus League play on Tuesday against the Athletics at 3:05 p.m. CT.
The groin soreness is not as serious as the hamstring issues Castro experienced which kept him out of Spring Training last year.
"Not even close -- I can play right now," Castro said. "I can play 100 percent right now. I feel a little tightness, and came in here and got a little massage and that's it. The tightness is gone. It's still early, and doesn't mean anything here. I don't want to push myself and get hurt here with two weeks left before the start of the season."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.