"It would be very difficult for him to be back before the end of the season," Renteria said Tuesday. "He's still wearing his boot, and he's not really doing any baseball activity. I think he's done a great job trying to push himself and come back before the season was over, and that's a credit to him.
"The jolt he took with that ankle was pretty good. He's done everything he can to try to put himself back on the map with us before the season is out. Right now, it'd be very difficult for me to see him back on the field."
Renteria said he didn't need to say anything to Castro about his season being over.
"The boot on his ankle is telling him," Renteria said.
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.