Castro began this season with a career .297 average in the big leagues. A two-time All-Star, he entered Sunday batting .234.
"I haven't seen him hanging his head or losing his confidence," Sveum said.
• Third baseman Luis Valbuena has played better than his stats.
"On a whole, from last year to this year, he's been so consistent, even though you're not seeing a .300 batting average," Sveum said of Valbuena, who is batting .247 entering Sunday. "The on-base percentage and the walks seem to always be there on a consistent basis, and the defense he's played has been as good as anybody at third base."
• Javier Baez, the Cubs' No. 1 Draft pick in 2011, made quite an impression in his Double-A Tennessee debut on Saturday, hitting a home run on the first swing of his first at-bat.
"It's always nice for anybody to go to another league and your first swing is a home run," Sveum said. "This guy still has to develop. It's not just home runs we're talking about, it's getting ready and getting completely developed to play at this level."
Baez led the Florida State League with 17 home runs while at Class A Daytona before he was promoted.
Meanwhile, Albert Almora, the Cubs' 2012 top Draft pick, had to leave Saturday's game with Class A Kane County because of hemorrhoids. He is listed as day to day.
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.