Arroyo was diagnosed with carpal tunnel syndrome in his pitching hand during the 2008–09 offseason. As a result, he missed games during the 2009 spring training, as well as being advised to stop playing guitar until the symptoms disappeared. After a sub-par first half of the 2009 season, Arroyo turned in an excellent second half, lowering his ERA from the 5's to the 3's, throwing multiple shutouts and complete games, and putting himself in position to be the Reds top starter in 2010 since Edinson Vólquez, the #1 starter in 2009, was out for the start of the season following Tommy John surgery. Arroyo finished the 2009 year with 2 shutouts, a 15–13 record, and a 3.84 ERA.