The Swiss star was deposed from the top ranking by Nadal in 2008 with the Spaniard also taking his Wimbledon crown after a five-year reign.
Federer will begin his new year in the unlikely surroundings of the Zayed Sports City at the Abu Dhabi International Tennis Complex where Nadal, as well as four other top 10 players, will battle for the $250,000-top prize.
"Never before have I started a tennis year as early as the one ahead. I will be back in action on January 1st," said Federer ahead of the January 1-3 exhibition tournament in Abu Dhabi.
"I'm looking forward to the tournament, which is taking place for the first time, as well as the entire season of 2009. There is such a large number of challenges lying ahead - facing them, working hard and giving my best to succeed is precisely why I love my job so much."
Andy Murray, Nikolay Davydenko, Andy Roddick and James Blake make-up the six-man field in the UAE.
Federer said he was taking a lot of positives from 2008 where he picked up an Olympic gold medal, in the doubles with compatriot Stanislas Wawrinka, as well as successfully defending his US Open title, his 13th Grand Slam triumph.
"Looking back at the past 365 days a lot of unforgettable experiences come to mind," Federer told his website. "But there are, of course, also the tough moments I had to go through. I faced an unexpectedly difficult training period and exhausting start of the season due to illness precisely 12 months ago.
"I spent a great deal of the year battling with the lack of practice and hours of training that I faced at the time."
Federer struggled with glandular fever at the start of the year and lost his Australian Open title to Novak Djokovic.
"So having played another three Grand Slam finals and having brought home the US Open trophy as well as reaching Olympic heights together with Stan Wawrinka makes me just the more proud.
"I was honored to receive the Laureus title as Athlete of the Year again and also lift the trophy at my home-tournament in Basel once more. These are some of the truly wonderful, emotional moments I had the privilege to experience."
Meanwhile, there seems to be no end to the Nadal success story.
The Wimbledon, French Open and Olympic champion was the subject of a marathon four-hour special aired by Spanish TV over Christmas, documenting his remarkable 2008 campaign.
After the three-day UAE event, Federer and Nadal will resume their competitive rivalry at the Qatar Open which starts in Doha on Jan 5.
n. 比赛,锦标赛,(中世纪的)骑士比武