"I think Castro is one of the young players who come around once in a while, and they can be as good as they want to be," Cubs manager Dale Sveum said Friday about the 22-year-old shortstop.
"The ceiling is very high, but it's still up to those individuals to make a difference on an everyday basis -- and not just as a hitter, but as a player and a winning hitter, and always making a difference in a ballgame to win ballgames."
Castro leads all National League shortstops with 93 hits and a .301 batting average, and his .437 slugging percentage ranks third. The Cardinals' Rafael Furcal led the latest All-Star voting results at shortstop, while Castro ranked third.
All season, Sveum has asked Castro to grade himself on a scale of one to 10 each day.
"He doesn't have a 10, but at least he's been good in games for the most part," Sveum said.
If NL All-Star manager Tony La Russa needed any recommendations, Sveum said he'd include outfielder Alfonso Soriano, who has 14 home runs in his past 40 games, starting May 15. That's the most in the NL and third most in baseball.
One of the Cubs' best options would have been Ryan Dempster, who is currently on the disabled list.
"He would've been a no-brainer if healthy the whole time," Sveum said of the right-hander, who has a 2.11 ERA in 12 starts.
The All-Star Game will be played in Kansas City on July 10 and can be seen on FOX at 8 p.m. ET.