Roger Federer and Rafael Nadal pose with their trophies after the Men's singles final match at the 2017 ATP Shanghai Rolex Masters. Getty

While Rafael Nadal sits atop the ATP rankings, his reign may not last much longer. No. 2 Roger Federer could still finish the year as the top tennis player in the world with the ATP World Tour Finals at O2 Arena in London looming.

It has been a fantastic year for both veteran stars, who have each won six titles and two Grand Slams after both failing to win one in 2016. Federer has 8,505 points and trails Nadal with 10,465.

On Sunday, Federer defeated Nadal 6-4 6-3 in the final of the Shanghai Masters. It was Federer's fifth win in a row over the Spaniard.

Nadal recently announced that a knee injury would force him to sit out the Swiss Indoors in Basel from Oct. 23-29. Federer could pick up 500 points in Basel, the city where he was born, and another 1,000 points for the Rolex Paris Masters from Oct. 30-Nov. 5.

The Nitto ATP Finals will take place from Nov. 12-19. Andy Murray, who won the ATP Finals in 2016, is No. 3 in the world and is followed by Marin Cilic at No. 4.

The biggest disappoint of the year has been Novak Djokovic, who is ranked No. 7. In July, the Serbian star announced he would be sidelined for the rest of the 2017 season due to an elbow injury that had forced him to withdraw from Wimbledon. Djokovic had won the ATP Final four straight years before his loss to Murray last year.

Stan Wawrinka has also seen a big drop in the rankings due to injuries. The Swiss star finished 2016 at No. 4 and is currently No. 9.

ATP Rankings

1. Rafael Nadal 10,465

2. Roger Federer 8,505

3. Andy Murray 5,290

4. Marin Cilic 4,505

5. Alexander Zverev 4,400

6. Dominic Thiem 3,935

7. Novak Djokovic 3,765

8. Grigor Dimitrov 3,590

9. Stan Wawrinka 3,450

10. David Goffin 2,885