For Roger Federer to regain the world No. 1 ranking, he will have to follow a carefully constructed blueprint while playing the best tennis he can muster.
Of that trio, Nadal is the least likely to climb to the World No. 1 spot due to a left-knee ailment that forced him to miss the second half of the 2012 season. Nadal has spoken about limiting the number of hard-court events that he enters, as the Spaniard's knees cannot handle playing on the surface too often.
Murray is currently ranked one spot behind Federer but is expected to be more of a year-round threat in 2013 now that he is a Grand Slam champion. Also, at just 25 years of age, Murray is at his peak physically and will play in more events than Fed.
However, Federer's biggest obstacle to get back to No. 1 is Djokovic, as the Serbian is currently in the top spot and has played brilliant tennis over the past two years.
The road back to No. 1 promises to be treacherous, but after an unlikely return to the top spot last season, Federer should not be counted out.