Rafael Nadal will return to world No 1 on April 2, despite not having played tennis since January, following Roger Federer's loss to qualifier Thanasi Kokkinakis in the second round of the Miami Masters.
Defending champion Federer will lose 990 ranking points following his early exit and that will drop him below Nadal when the next ATP rankings are published on April 2 following the conclusion of the action in Miami.
Nadal has lost 600 points by not competing in Miami, where he was runner-up 12 months ago but he will be on 8,770 points after Miami, 100 ahead of Federer.
It will be Nadal's fifth time as No 1 in the sport. He had regained the spot for the first time in three years in August but had lost it to Federer in February.
Nadal has not played since retiring hurt from his quarter-final against Marin Cilic at the Australian Open, and he suffered a leg injury during training that forced him to sit out Indian Wells and Miami, the first Masters tournaments of the season.
The Spaniard is expected back for the start of the clay court season, which begins with the Monte Carlo Masters on April 16.
Meanwhile, Federer will not play again competitively until June after his second loss in six days as he confirmed he will for the second successive season sit out the clay court action and not take part in the French Open.
Federer confirmed the plan after falling 3-6, 6-3, 7-6 to Kokkinakis.
Of the defeat, which came after he lost in three sets to Juan Martin del Potro in the Indian Wells final last weekend, he said:
"Sometimes you have these matches. Sometimes you find a way through. I just couldn't get it done today.”
His mood contrasted sharply with an ecstatic Kokkinakis.
“When I feel like I am playing on my terms, I don't think there's too many people who can go with me.”
Federer will look to rest up ahead of challenging for a ninth Wimbledon title in July.
He could be back as No 1 by then, however. Nadal won 24 of his 25 matches on clay last season, including winning a 10th French Open title, and has 4,680 points to defend and if he has an early exit at any of the events on the clay circuit then Federer will leapfrog him.