The 2013 tennis season is beginning but not for Rafael Nadal. After the knee problems that kept Nadal out of the courts in the last semester of 2012, now, just while he was scheduled to start competing, a stomach virus defeated all hope for him to play the first Grand Slam of the year. Currently at number four in the ATP Rankings with 6,690 points, Nadal him most probably lose several positions by January 28th 2013, the day when the 1200 points Nadal gathered as the runner up in last year’s Australian Open final will be dropped from the ranking.
David Ferrer, currently number five in the ranking and only defending 360 points in the Australian Open, for instance, will definitively end January above Nadal’s score.
In the meantime Novak Djokovic won the exhibition tournament in Abu Dhabi (against Nicolas Almagro) and Li Na defeated Viktoria Azarenka in the exhibition tournament of Hua Hin (Thailand).
The first official tournaments are about to begin. This is the official ATP calendar for December 2012:

DECEMBER

	30.12.2012	Brisbane International Brisbane, Australia	Hard	$ 436,630 ($ 486,000)	SGL 32 DBL 16	2011 Champions =>	Singles : Andy Murray Doubles : Daniel Nestor, Max Mirnyi
	31.12.2012	Aircel Chennai Open Chennai, India	Hard	$ 385,150 ($ 450,000)	SGL 28 DBL 16	2011 Champions =>	Singles : Milos Raonic Doubles : Janko Tipsarevic, Leander Paes
	31.12.2012	Qatar ExxonMobil Open Doha, Qatar	Hard	$ 1,054,720 ($ 1,110,250)	SGL 32 DBL 16	2011 Champions =>	Singles : Jo Wilfried Tsonga Doubles : Lukas Rosol, Filip Polasek

And these are the WTA tournaments that start the women season 2013: