The race to become the end of year number one in men's tennis is hotting up after Rafael Nadal announced he would not be playing at the Swiss Indoors tournament in Roger Federer's home town of Basel.
Nadal said he has been carrying a slight knee injury, which he felt during his defeat by Federer in the Shanghai Masters final. He now wants to rest it with the climax of the season in mind.
A statement by the tournament director in Basel said: "After seeing his team doctor in Barcelona, the world number one sadly had to pull out of the Swiss Indoors Basel. According to his doctors, the Spaniard suffers from overstressing of the knee."
With Federer picking up more points in Shanghai and hoping to win before his adoring local fans, there is now a real chance the Swiss superstar could snatch the year-end number one spot.
The Paris Masters offers 1,000 points to the winner and then the Nitto ATP World Tour finals could prove decisive in crowning the top dog for 2017.
Fans booking corporate hospitality for the event at London's O2 Arena will have good reason to be excited by the sudden rise in plot tension. Until Shanghai, it seemed the French and US Open champion would almost certainly be ending the year looking down on the rest. However, Nadal's lead is now down to 1,960 points and with 500 available in Basel, Federer could be within striking distance if he can win in his own back yard.
A critical factor in the equation could be the success Federer has had in his meetings with Nadal this year, which began with his Australian Open final victory.
Nadal still leads the head-to-head between the pair 23-15, but his last win over Federer came in 2014, at which point the margin was 23-10. Most significantly, Federer has won all three of their encounters this year. If they meet again in the final at the O2, it could be the second year in a row in which the end of year number one position is on the line in the very last match.
While this pair have dominated 2017, the event will not be all about them. The race to fill the other six qualifying places has been tightening up, with Alexander Zverev and Dominic Thiem having clinched their spots.
At present, the other four qualifying places are occupied by Wimbledon finalist Marin Cilic, Grigor Dimitrov, Stan Wawrinka and David Goffin. However, with Wawrinka missing the rest of the season with injury, the man currently occupying the last place is Pablo Carreno Busta.
What makes the situation particularly perilous for Carreno Busta is that he won the 2016 Kremlin Cup, so if he cannot repeat that feat he is vulnerable to a surge of form from those just below him, chiefly Sam Querrey and US Open finalist Kevin Anderson.
Tomas Berdych and Nick Kyrgios also have over 2,000 points this year and cannot be ruled out if they finish the season well.
In the doubles, British fans can cheer on Jamie Murray and his Brazilian partner Bruno Soares at the O2, with the pair clinching their spot in the finals last weekend.
Image: Getty, from Keith Prowe subscription