Djokovic physically tough enough?

Question

Credit where credit is due, a clearly unwell Novak Djokovic stayed on court in his Australian Open 2010 quarter-final against Jo-Wilfried Tsonga until the bitter end. But with a past record that includes withdrawing in the quarters at Melbourne in 2009 due to heat exhaustion among others, the question must be asked. Is Djokovic physically tough enough to go toe-to-toe with his fellow top ten players in the second week of a Grand Slam?