I can't see Djokovic doing the CYGS in 2013. The AO surface and Australian climate (or lack thereof) clearly favor his style. The grass at Wimbledon and clay at RG, have very different properties which don't help him.
I think Wimbledon is his real challenge. At Wimbledon, even mediocre movers can blow beastly-grinders like Djokovic off the court. At Wimbledon, you really don't need a ton of fitness -- like the other slams. You need solid serving and the ability to constantly rally with low bouncing balls.
If there's a guy who can do it, I think he could... but I would be highly surprised if he pulled it off. As good as he is, I just don't see him having enough variety in his game, yet.
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