CHICAGO -- The Cubs placed right-hander Cade Horton on the 15-day injured list Saturday because of a rib fracture, the team announced, eliminating any chance of him pitching in the wild-card round next week.
Horton, 24, initially injured himself coughing while ill last week in Cincinnati. He left his last start Tuesday after two innings.
Imaging showed an issue in his back/rib area, but the Cubs thought they could move forward despite the ailment. Horton played catch Friday and Saturday before the Cubs said he would be put on the injured list.
"He went out and threw today. He could really feel the rib. There was discomfort," Cubs president of baseball operations Jed Hoyer said. "He couldn't let it go and pitch the way he needed to."
Horton had emerged as the Cubs' best starter despite being a rookie. He was 8-1 with a 1.03 ERA in 12 second-half starts before leaving his final outing early on Tuesday against the Mets. He is the favorite to win the National League Rookie of the Year award but won't be eligible to pitch in the postseason until at least Game 5 of the division series.
Hoyer said he didn't have an exact timeline for Horton's return.
The Cubs will face the San Diego Padres in the wild-card round, beginning Tuesday. Horton was a possible Game 1 starter, which means the Cubs are likely to turn to Matthew Boyd for that role with Shota Imanaga also in play. Right-handers Jameson Taillon or Colin Rea could get a start as well after both have had strong finishes to the season.