3 Cubs players who won’t be on the roster by September 1
By Tim Boyle

2. Cubs roster won’t have Kervin Castro on it for long
Kervin Castro is only 23 so maybe his rough beginning with the Cubs isn’t the end. He’s a young arm and definitely someone they should give a shot to next spring unless he ends up as a complete disaster through the end of this season.
A demotion for Castro might not have all that much to do with his performance, though. Because he does have minor league options and the Cubs will need fresher arms through the end of the month, he’s a top candidate to get demoted.
The Cubs bullpen lacks veterans post-trade deadline but they do have a couple of guys with more experience than Castro. Castro is the youngest of the relief pitchers and one of the weaker-performing ones at the moment. Although he’s hardly the only option to send back to the farm in favor of a more well-rested option, we could expect the Cubs to turn to the least experienced guy.
Castro is competing against his fellow bullpen mates but also a permanent candidate to get sent down regardless. Because rosters only expand for two additional players in September, the Cubs could keep him on a shuttle back and forth between Triple-A and the majors for the rest of the season.