 On 6 July 2009 following his release from Millwall, Forbes agreed to join Grimsby permanently on a two-year deal.During the 09/10 season, Forbes struggled to break into the first team and was eventually ruled out for a lengthy period after breaking his leg.This coupled with playing second fiddle to other players and the failure to consistently earn a place in the team meant that he would only feature in 13 league matches throughout the entire season.