ATP Finals: Federer Gets Tougher Group; This Is How Djokovic Can Reclaim No. 1 Rank

Novak Djokovic and Roger Federer have been drawn in the same group at the ATP World Tour Finals, which starts Sunday at London's O2 Arena.

Apart from Djokovic, who has won the tournament five times and six-time winner Federer, the group also includes Dominic Thiem and Matteo Berrettini.

The other group boosts of World No. 1 Rafael Nadal, Daniil Medvedev, Stefanos Tsitsipas and Alexander Zverev. Considering Nadal's current fitness, there were rumors that the Spaniard might not play in London.

Nadal, who is yet to have the decorated ATP Finals trophy on his CV, said Tuesday that he has plans to compete in the year-ending big showdown, even though he has pulled out of last week's Paris Masters.

In an interview Tuesday, Nadal revealed that an MRI scan has confirmed just a "small" abdominal injury that forced him out of Paris Masters' last-four and nothing major.

Despite not winning the Paris Masters, which Djokovic eventually won, Nadal overtook the Serb at the top of the ATP rankings. However, there are chances that Nadal might not end the year as the No. 1 player.

If Nadal does not play or fails to win a round-robin game at the ATP World Tour Finals, Djokovic will reclaim the top spot if he wins two group stage matches and reaches the final. In another scenario, if Nadal does not reach the semi-finals and Djokovic wins the tournament, the latter will get back to the top.

The ATP World Tour Finals are the season-ending championship in which the year's top eight players compete and the tournament has been played at London's O2 Arena since 2009. The players are divided into two groups with the top two in each of the groups. There are three round-robin rounds before the semi-finals and the grand final.