On 24 February, Mitchell was stretchered off in a 2–2 draw Notts County. Scans revealed fractures to the tibia, fibula and ankle surfaces which would require 18 months of rehabilitation. He returned to action in a 2–1 defeat to Cardiff City on 26 August 2008, but the match proved to be his final match for the Dons. Later that month, Mitchell signed for Barnet on loan as part of his recovery process. On 30 August, he made his debut during a 5–1 defeat to Chester City. A week later, he completed 90 minutes in a 4–2 defeat to Dagenham & Redbridge in the Football League Trophy. Mitchell made a further two appearances, with his final coming in a 1–1 draw with Morecambe on 13 September.