Dempsey's professional footballing career has been dogged by injuries. In 2008 he suffered a leg stress fracture[5] and in 2011 he tore his knee anterior cruciate ligament (ACL) in round four and needed a knee reconstruction.[6]
In May 2013, he was suspended from the main playing group for breaching team rules, and was forced to train with the VFL team.[7] In August, he tore his hamstring tendon[8] and missed the remainder of the season.
At the conclusion of the 2016 season, he was delisted by Essendon.[9]