 A long term member of the leadership team, and widely regarded as having one of the best football brains in the game, Whitnall first took over the captaincy of the team during Anthony Koutoufides' hand injury in 2006, and became the full-time captain in 2007 after Koutoufides relinquished the position.However he struggled in 2007 with ongoing problems with a degenerative condition in his knee.At the completion of the 2007 season, concerns by the club about his degenerative knee being able to stand up to the pressures of AFL football forced Whitnall into retirement, bringing his 11-season, 216 game career at Carlton to an end at 28 years of age.