CHICAGO -- As much as he wanted to return from an injury, Chicago Cubs All-Star shortstop Starlin Castro's season is officially over.

"It would be very difficult to be back before the end of the season," manager Rick Renteria said Tuesday afternoon. "He really hasn't done any baseball activity."

Castro is still in a walking boot after spraining his ankle sliding into home plate earlier this month. He hasn't played since Sept. 3 but that doesn't take away from his performance, which has been among the best at his position this season. Castro hit .292 with a .339 on-base percentage to go with 14 home runs and 65 RBIs. That's a far cry from his .245 batting average in 2013. Among his other improving stats, his strikeouts-to-walks ratio dropped from 4.3 to 2.8.

Castro should be in the conversation for comeback player of the year. His WAR (Wins Above Replacement) improved from -0.6 in 2013 to 2.0 this season and that was with missing games because of injury and time on the bereavement list.

Many will wonder if we've seen the last of Castro as a Cub as his trade value may never be higher, and the Cubs are loaded with middle infielders. But the value of a three-time All-Star -- at arguably the most important position on the diamond -- can't be over looked. Time will tell if Castro is here, or another young player is moved instead.