Roger Federer will begin his bid to regain the world number one position from Rafael Nadal when the 2009 men's circuit gets underway at the Qatar Open from Monday.
The opening week of the ATP World Tour could see the two great rivals meet for the first time since their sensational Wimbledon final six months ago.
However, the duo will be wary of the threat posed by Andy Murray after the Scotsman beat both players to win the 250,000-dollar Abu Dhabi exhibition event on Saturday.
Last year's four-hour 45-minute Wimbledon epic was won 9-7 in the final set by Nadal, though it was Federer who produced the most memorable quote.
"From my point of view many people left feeling sorry for me instead of being happy for Rafa - which hurts," he said.
An ATP poll of 65,000 people recently showed that 44 percent believe Federer will regain the top spot he held for a record 237 weeks, and the Doha event could indicate whether they are right.
Against that, 34 percent thought Nadal would go on to become the first left-hander to finish world number one in back-to-back years since John McEnroe in 1981-84.
Last year the muscular Spaniard won the most titles (eight) and the most matches (82) and he is still only 22. This suggests he may not yet have reached his peak and should have more years left at the highest level than his 27-year-old rival.
"I believe he could stay number one easily for two or three more years," Nadal's agent, Carlos Costa, said. "He will have a hard battle this year, but he is the best player right now."
Costa therefore reckons Federer will not regain the pinnacle. Only one man previously - Ivan Lendl 20 years ago - has won the world number one ranking back.
Some people paint an even gloomier future for Federer, believing the loss of two Grand Slam titles in 2008, plus the failure to win any Masters Series, and a defeat at the Olympics indicate psychological and physical decline.
Nadal is not one of those.
"Federer is Federer, and when people said he is finished, I've always denied it - not only because I knew he was going to win big tournaments again, but also because I considered him the best player of all time," he said.
Indeed, it may be Nadal's physical shortcomings which are the more significant. Injury prevented him from taking part in either the ATP Tour year-end championships in November or the Davis Cup final in December, and there are long-term worries about his knees.
But after his three-set defeat to Murray on Saturday in neighbouring UAE, Nadal said he was happy with his health.
"The final was two hour, 45 minutes of high-quality, and I'm feeling very well," said the Spaniard.
Many people see Murray as the greatest threat in 2009.
Murray is the only player apart from Nadal with a superior head-to-head record against Federer, and he may also be spurred on by being next week's defending champion.
"It's a great start to the year," said Murray after his 6-4, 5-7, 6-3 win over Nadal on Saturday.
"I worked very hard on my fitness and game in November and December and both Rafa and Roger played great tennis, so I am delighted that I could beat them."
1, Rafael Nadal (Spain); 2, Roger Federer (Switzerland); 3, Andy Murray (Britain); 4, Andy Roddick (United States); 5, Igor Andreev (Russia); 6, Dmitry Tursunov (Russia); 7, Philipp Kohlschreiber (Germany): 8, Mikhail Youzhny (Russia).