"I think [Saturday] I'll go to the Minor League [game] and get some at-bats -- four, five at-bats -- and hit every inning," Castro said after batting practice on Friday.
Does he have enough time?
"If you go every other day and go to the Minor Leagues and take five at-bats, I think I'll be all right," he said. "I can be there."
The Cubs have not talked to Castro about the possibility of opening the season on the disabled list.
"I don't think that will happen, because I've really progressed and I think I'll be all right," he said.
"We're trying to get him some at-bats, possibly in the Minor Leagues first, leading off, things of that nature, and trying to get him in baseball shape," Renteria said Friday. "He's been doing a lot of activity, but getting him out there, standing, playing five, six innings is important to us. We're going to try to progress him as quickly as possible."
Do the Cubs have a backup plan?
"Not even a consideration at this point," Renteria said. "He's doing well."
However, the Cubs have had Darwin Barney play shortstop this spring and also have Emilio Bonifacio and Donnie Murphy as infield options as well.
"Right now, it's Friday, and [Castro] went through everything extremely well [Thursday], and I have nine days left," Renteria said. "I've got to set up a schedule for him to participate before we can determine [if he'll be ready]."
Castro said he's had no discomfort doing the infield work and light baseball activities so far, but he has not been on the field for more than a few innings, so his game conditioning is not quite there. The shortstop is coming off a disappointing season in which he batted .245, and he has said he wants to get back to being the two-time National League All-Star who collected 207 hits in 2011.
"He's a guy who we all know physically we have to get in a particular type of shape," Renteria said. "Mentally, if he's in a good state of mind, anybody who has a sense of confidence and focus and determination, you have the ability to do a lot of things. Hopefully that will play into his ability to overcome this little setback that's occurred this spring."
Last spring, Castro strained his left hamstring and only missed two weeks. He's been out nearly three this March.
"I know he wants to play," Renteria said. "It affected him. He hated this setback this spring, obviously. He wants to show everybody and have a comeback-type season. He looks like he's ready to get back out there on the field."