Andy Murray may currently be in the top spot, but given the amount of ranking points he has to defend it is likely to be either the Swiss player or the Spaniard who ends 2017 on top.
Roger Federer v Rafael Nadal for No 1 ranking the story ahead this year in tennis
There are a lot of reasons to feel like 2017 could be mistaken for 2007.
Roger Federer heading to the US Open later this month targeting a third grand slam title of the year.
The Swiss player likely to spend the remaining period of the year duelling for top spot in the rankings with arch-rival Rafael Nadal.
The latter scenario is not happening yet, given it is still Andy Murray sitting in the No 1 slot, but Federer v Nadal is coming.
Murray is sitting out the action at the Canadian Open this week as he continues to rest the hip injury which hampered him at Wimbledon.
With Novak Djokovic and Stan Wawrinka both ruled out for the rest of the year as they recover from injuries, the way is open for the Federer and Nadal renaissance to continue, this time for the No 1 ranking.
Nadal, 31, the world No 2, could go back there next Monday when the fresh list is published by the ATP.
He is only 285 behind Murray's rankings points total of 7,750, and reaching the semi-finals, which has a reward of 360 points, would put the Spaniard on top of the pile for the first time since June 2014.
Even if Federer, 35, the world No 3, is triumphant in Montreal for the first time since 2006, he cannot reach No 1 this week, given he is 1,205 behind Murray.
Murray did not play in Canada last year due to his Olympic commitments in Rio so he will not lose any ranking points despite being missing in action.
But business will pick up as the month goes on, and effectively it is going to come down to who has the stronger hard-court season between Federer and Nadal as to who will have the No 1 spot going into the closing months of the year.
Neither Nadal or Federer have many points to defend in the final four months of action this year, in Federer's case he has no points to his name to match, given he did not play again in 2016 after his semi-final loss to Milos Raonic at Wimbledon.
So, even if in some freak set of circumstances in which Federer did not win another match this year, he would at the very worst be on his current total of 6,545.
Nadal only has 405 points from 2016 still to defend, starting next week in Cincinnati where he was knocked out in the third round last year.
Murray, even before taking into account his current injury issues, is highly unlikely to finish the year as No 1.
His form has been poor in 2017 with the Dubai Duty Free Tennis Championship in March remaining still his only title won this year.
So to expect him to match his great end to 2016, which saw him win four ATP titles in a row before winning the ATP World Tour finals is something only the most ardent Murray fan will believe can happen.
So he will drop below 7,750 realistically, so both Federer and Nadal can be confident of overtaking him very soon, possibly both by the end of next week at the Cincinnati Masters.
Federer has to be favourite to end the year as No 1 given his majestic form and the fact he has lost only twice all year so far.
He should be rested for Montreal, and given how well he played on the hard court surface earlier in the year in winning the Australian Open then in Indian Wells and Miami, it is hard to see him not racking up a lot of points over the next couple of weeks and then at the US Open.
Nadal should not be discounted either, considering he was runner-up to Federer in Melbourne and Miami, but if Federer is not No 1 for the first time since October 2012 at the very latest by the end of the action in New York it will be a shock.
It would be a fitting final touch on a year when Federer has reminded everyone that age is just a number as he continues to confound the tennis world with his performances on court.