"I don't want to be, 'OK, I'm good,' and then get hurt again," Castro said. "I want to be good for 162 [games]."
Stewart, sidelined since Feb. 22 with a sore left quad, was able to swing a bat and play catch on Saturday, and has continued to add some baseball activities to his schedule.
"We've come this far and I don't want to take a chance at a setback now," Stewart said. "We're taking it each day and seeing what kind of progression we make from the day before and going from there."
The Cubs expected him to be sidelined 10 to 14 days before he could start hitting.
"Honestly, I am pretty pleased with the progress we've made because in the beginning, it was hurting pretty bad," Stewart said. "I thought it would be longer than that. I'm pretty pleased with where we're at now."
In a perfect world, Stewart would get 70 at-bats in Spring Training. To do that, he'd have to play every game, every day, every inning.
"If that's what it takes, that's what it takes," he said.
Cubs manager Dale Sveum had talked to Stewart about going to Minor League camp to get more at-bats even before he was injured. That may be an option now, too. Stewart was limited to 55 games last season because of a sore left wrist which eventually needed surgery.
"It is very frustrating," Stewart said about being sidelined. "I worked hard this offseason, spent a lot of time away from my family this offseason, going back and forth from California to North Carolina. It is tough and I guess the only positive is that the season is six and hopefully seven months long. It's better if you're going to be hurt this time of year, and not something to take you away from meaningful games in the middle or latter part of the season. Hopefully, it won't be too much longer."
The Cubs do face some decisions regarding Stewart. His $2 million contract is non-guaranteed, which is not unusual for an arbitration-level player, but there is a March 16 deadline. If the Cubs decide at that date that Stewart isn't ready, they can release him and will be obligated to pay one-sixth of his salary ($333,333). If he's released after that date and before the regular-season opener, the Cubs would owe Stewart $500,000.
"That's the last thing I want to really think about," he said. "I had such a great relationship with Theo [Epstein, Cubs president of baseball operations] and the front office over the winter. I trust them and trust that they brought me back to be a part of the team.
"Hopefully, I don't have to start the season on the [disabled list] or even with another team," he said. "I trust them that everything we talked about before I came back to the Cubs is what they believe in and they want me to be a part of the organization here."