Horton, 24, threw a fastball to Bo Naylor before ultimately leaving the game after manager Craig Counsell and trainers visited him on the mound. This was just Horton's second start of the season, as he managed to get through the first inning without allowing a hit.
Reporter Taylor McGregor said that Horton was in tears as he entered the team's clubhouse.
Horton said in the post-game interview that he had originally felt discomfort in his wrist that moved up to his forearm and will receive imaging on Monday.
He tossed 6.1 innings in his season debut on March 28th against the Washington Nationals, giving up two earned runs on four hits with one walk and four strikeouts.
The promising young starter made his MLB debut last season with the Cubs and immediately showed out. He finished with an 11-4 record and 2.67 earned run average through 22 starts (23 games). He totaled 97 strikeouts, 95 hits, and 33 walks through 118.0, finishing as runner-up to Drake Baldwin (Atlanta Braves) in National League Rookie of the Year voting.
The Cubs are currently 3-4 on the season, sitting in last place in the NL Central division. Game two of their series against the Guardians begins on Saturday, 7:15 p.m. Eastern time.