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Double Olympic champion Alistair Brownlee says he may not return to triathlon for the 2020 Tokyo Olympics.
The World Triathlon Series starts in Abu Dhabi on Friday but Brownlee, 28, is not racing as he prepares to step up to the longer half-Ironman distance.
The Yorkshireman claimed triathlon gold at Rio 2016, defending his title from London 2012.
"There's a chance I could never be at an Olympic Games again but to say I'll never do it is impossible," he said.
"The Olympic Games are just fantastic and I'd definitely love to be there but the course in Tokyo is going to play a big part in terms of whether I feel I can go there and win.
"It's going to be a case of sitting down at the end of 2018 and weighing it up - am I enjoying the long distance stuff? Am I still able to be competitive enough to win a medal in Tokyo?"
Brownlee will defend his World Series title in Leeds on 11 June, but that is his only confirmed race so far this season, while brother and Rio silver medallist Jonny begins his campaign from the second race in the Gold Coast on 8 April.
For the rest of the year, Alistair Brownlee will combine standard Olympic length events - 1.5km swim, 40km on the bike and 10km run - with half Ironman distance competitions, also referred to as Ironman 70.3 in reference to the total number of miles covered.
He added that the Ironman 70.3 World Championship in September is an "obvious" target as he builds up to the full Ironman distance, which he says has always been on his "bucket list".
"Ironman has got to be one of those things you always want to do - it's like the London or Boston marathon of triathlon," he added.
No Gomez, no glory?Alistair Brownlee won gold at Rio 2016 but believes the absence of rival Javier Gomez detracted from his achievement
The two-time gold medallist added that his Rio 2016 win was slightly marred by the absence of long-term rival and London 2012 silver medallist Javier Gomez, who withdrew from the Games after breaking his elbow in a cycling accident.
"It definitely took a bit away from my gold in Rio that Gomez wasn't there," said Brownlee.
"You want to be there in your best shape and race the best athletes in their best shape - we were fortunate to have that in London and it would have been fantastic to have had that in Rio as well but what happened happened.
"But on that day, on that course, I'm fairly confident I'd have had him anyway."
With Gomez, 33, back from that injury, Brownlee expects the Spaniard to challenge for the World Series title, alongside compatriot and current champion Mario Mola, 27.
And the older Brownlee expects Jonny, 26, to complete the podium and says his brother could claim the title with "a bit of luck and a fair wind behind him".
Marathons and cycling next?
Alistair Brownlee says he may have been "bored" returning to World Series racing, having experienced the "same kind of racing against basically the same people for the last 10 years".
However, he adds that he is motivated by his new goals, which could include competing in 10,000m running races and the marathon.
"I now have an opportunity to try these other things without hurting my chances if I do decide I want to compete in four years in Tokyo," he said.
"I thought about a lot of things after Rio. I definitely want to run a marathon and that might be in the not too distant future.
"The other obvious thing is cycling and trying to make a wholehearted jump into being a professional cyclist but although that's possible, I'm very aware that in that arena and in running, I can be good and get to a level where I could be professional, but never to a level where I can win stuff.
"I still feel like I want to be the best at what I'm doing so that's why I'm choosing things I feel like I can win."