Federer in February became the oldest top-ranked men's singles player in the history of the sport, dethroning arch-rival Nadal.
The Spanish ace though has an opportunity to regain the top spot despite having withdrawn from Indian Wells and the subsequent Master's 1000 tournament in Miami, which starts later this month, with a hip injury that also forced his withdrawal from ATP 500 tournament in Acapulco last month.
Federer is gearing up for a title defense in Indian Wells with a lead of 600 ranking points over second-placed Nadal, who has 9,460 points. However, the 20-time Grand Slam champion needs to reach at least the semi-final of the Master's 1000 tournament in order to retain his at the top.
In Master's 1000 tournament, the winner gets to retain 1,000 points, the runner-up gets 600 points while the semi-finalists hold 360 points each.
Nadal, who bowed out in the Round of 16 after losing to Federer in 2017, will drop only 90 points.
"I guess, it's an extra motivation. I am aware of it, the rankings. It wouldn't hurt me in any way because Rafa [Nadal] would deserve it again because he has had a fabulous season himself, but I'll try," Federer told ATP World Tour.
"I am disappointed for Rafa that he is not here. I had a great trip to the Indian Wells and Miami last year so I have a lot of points to defend. There is a bit of pressure maybe this week but I have defended my points for the last 20 years so there's nothing new there.
"I will try to give it my best and hopefully have a good tournament."
Federer handed easy draw
Federer, who started the current season on a high by winning the Australian Open and Rotterdam Open, starts as the top seed at Indian Wells Masters. Following a first-round bye, the 36-year-old will face world no 67 Federico Delbonis in the Round of 64 on Saturday, March 10.
Having been handed an easy draw, Federer is likely to face fifth seed Dominic Thiem in the quarter-final. The Swiss ace might face comeback man Novak Djokovic in the title-clash if the latter manages to get past the likes of Marin Cilic and in-form stars Juan Martin del Potro and Alexander Zverev in his half.