Rafael Nadal has been absent from tennis since July, when he was stunned by then-World No. 100 Lukas Rosol at the second round of Wimbledon. The rest of the tennis world has moved on admirably well without the player who was ranked No. 2 before his lengthy layoff.
Andy Murray shed the label of being unable to play in big matches; the Scot made the finals of Wimbledon, won the Olympic Gold Medal and then, after losing four previous major finals,  finally captured the U.S. Open last month.

Roger Federer, considered by many to be in a downfall, played brilliantly en route to a seventh title at the All-England, as he was able to avoid a showdown with nemesis Nadal.
Still, tennis needs him to come back. The Spaniard, now ranked No. 4, is expected to return for an exhibition tournament at Abu Dhabi in late December.

Rafa's matches are always very high quality, and he has been a part of great rivalries with fellow top players Federer and Novak Djokovic. Many fans are impatiently awaiting Nadal's return to see what he can do after missing such a long period of time.
In 2012, Nadal played well before Wimbledon, winning Roland Garros for the seventh time and proving that he is second to none on clay court. He seemed more intent on taking over points when he was facing Djokovic, who had punished Nadal in 2011, capturing all seven of their head-to-head meetings.

Rafa took three consecutive matches from the Serb after dropping a five-set classic in Melbourne in January 2012. He was clearly playing some of his best tennis when not serving, as Rafa, despite playing 33 less matches than Djokovic, still had three more return games won, and his 38 were the best on tour.

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However, outside of the clay-court season, Nadal was not at his best. He only made one final (Australian Open) and lost before the semis in both his grass-court appearances.
Nadal has missed so much time, that it should be safe to assume that he can come back near-full strength. One of the Spaniard's previous problems has been rushing his return from his injuries, which is pretty clearly not going to be an issue this time around.
On the flip side, this is one of Rafa's most prolonged absences. After chasing him for years, the World No. 4's violent style of play may have finally caught up to him.
I would assume that by the time Nadal is back, he will be very close to, if not 100% healthy.
Overall, however, the native of Mallorca has struggled when he is not on his beloved red dirt. His last title victory that wasn't on clay came in Tokyo 2010, at the close of his career year.
Because of this, I would expect the majority of Rafa's good results to come in the spring, when the clay-court swing hits the tennis calendar.

Nadal seemingly erased the thought of him being a "one-trick pony" after his epic victory at Wimbledon in 2008, but that label has crept up back to Rafa.
Rafa seems to partially believe this himself, as his uncle and coach, Toni, recently confirmed that his nephew will play the Mexican Open at Acapulco in February, meaning he will skip Rotterdam. True, Nadal has not played at the Dutch tournament since 2009, but it was usually for rest, not in order to play another tournament. Indian Wells, an ATP Master 1000 title, opens play the day following the end of Acapulco.

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It remains unclear whether or not the Spaniard will appear in California, although it must be assumed that Rafa will play.
I think that it is fair to expect a 2013 similar t0 2012 from Nadal, minus the Wimbledon collapse and the three- or four-month break. He will continue to prove that he is the greatest clay-court player ever, but his other results will be less than satisfactory.
Expect an eighth Roland Garros title, and probably one other Grand Slam final, as well as victories in Acapulco, Barcelona and Monte-Carlo in addition to possible trophies in Madrid and Rome.
In other "minor" tournaments, I don't see Nadal getting any wins, but he might make a few deep runs.
The year 2012 may have proved that Nadal is actually the fourth-best player in the world, after being clearly in the top two from 2007 until midway through this year.
Federer's jump to No. 1 in the ATP rankings may be slightly exaggerated, but he still had a very resurgent season. However, his level of play dropped off after Wimbledon, and he won't hold on to the top slot much longer.

Djokovic has proved that he can play with Nadal head-to-head, and his drop-off from the superb 2011 form is greatly blown out of proportion. He will contend at every major next year.

It may be a bit of a stretch to consider Murray ahead of Nadal, but his victory at Flushing Meadows was clearly a turning point, and he has made it very clear that tennis has a "Big Four" over the past three months. He should be in the running for World No. 1 if he has good showings in 2013.
He can still dominate the head-to-head against Federer, and matchups with Djokovic will be about split.
Andy Murray, who had a coming-out party of sorts in 2012, will close the head-to-head gap between him and his Iberian rival, because his confidence is now at an all-time high.
I think the long period of time away from tennis could benefit Nadal, but with the rest of the world catching up, don't expect much more than what you saw in 2012.

Source: http://bleacherreport.com/articles/1375283-rafael-nadal-what-can-we-expect-from-the-spaniard-when-he-returns