Castro was expected to get into Thursday's game, replacing Theriot after three or four innings.
"There will be plenty of time for these kids to play," Piniella said.
One of the issues to be resolved in the next four-plus weeks is the leadoff spot, and Piniella plans on rotating Theriot and Fukudome in the No. 1 slot. The Cubs would like to pick one for the regular season.
"Neither of them will steal 40 bases," Piniella said. "I would try to stay as constant as possible, to be honest. Let's keep an open mind and see what Spring Training does for us."
Randy Wells, who won 12 games in his rookie season last year, will start on Thursday, and was to be followed by Sean Marshall, J.R. Mathes, Mike Parisi and Esmailin Caridad. Carlos Zambrano will start Friday against the D-backs, Carlos Silva on Saturday against the White Sox, and Jeff Samardzija and Tom Gorzelanny will start Sunday in the first of five split-squad games. Ryan Dempster was slated to start Monday in Phoenix against the A's.
Thursday's game will be aired on Gameday Audio at 2:05 p.m. CT. Saturday's tilt will be on MLB.TV and Gameday Audio at 2:05 p.m. Sunday's split-squad matchup against the White Sox will be on MLB.TV, Gameday Audio and a Web cast on cubs.com.
"We've got some decisions to make here in camp, we really do," Piniella said. "They're decisions on key spots: the rotation, the bullpen and our bench."
As far as injuries go, the Cubs are relatively healthy. Ted Lilly, coming back from arthroscopic surgery on his left shoulder, threw long toss on Tuesday. Angel Guzman, who had been bothered by soreness in his right shoulder, was doing well with his throwing program.
Jeff Gray, however, was not expected to throw off the mound until early next week. Sidelined with a groin strain, he apparently still felt something during a workout Monday.