Dempsey's professional footballing career has been dogged by injuries. In 2008 he suffered a leg stress fracture and in 2011 he tore his knee anterior cruciate ligament (ACL) in round four and needed a knee reconstruction. In August 2013 he tore his hamstring tendon, and will miss at least four weeks leading into the finals.
Dempsey had a rocky start to the 2014 season after struggling with injuries, then unfortunately being suspended from the main playing group after a progression of behavioral issues. However Dempsey did his time and came back into the senior side and looked to build for a big second half of the season. His run and carry and precision skills continued to be vital across half-back for the Essendon side.