Dieker continued his football career at Southern Illinois. Dieker was a 4-year starter for the Salukis, going 20-9 during that time.[2] He helped the Salukis to two conference championships, and was the 3rd quarterback in school history to pass the 5,000-yard mark for his career.
Dieker signed with the Cleveland Gladiators for 2013. Dieker was serving as the backup to starter Brian Zbydniewski, when Zbydniewski went down with injury, Dieker became the starter for the Gladiators. With the team's playoff hopes dwindling, Dieker delivered a big win for the Gladiators, scoring 8 touchdowns in a win over the Pittsburgh Power, helping keep the Gladiators' playoff hopes alive.[7] He became the starting quarterback in 2016 after the departure of Shane Austin. Dieker was injured in the first game of the 2016 season. On June 10, 2016, Dieker was placed on reassignment.
Dieker was selected by the Beijing Lions in the 2016 CAFL Draft and was the backup to Luke Collis during the 2016 season. On November 6, 2016, during the first China Bowl, Dieker played wide receiver due to an injury to James Romain. Dieker caught 9 passes for 107 yards and one touchdown as the Lions beat the Qingdao Clipper by a score of 35–34. He also scored a rushing touchdown during the game.[8]