Nadal has been sidelined since a second-round loss at Wimbledon because of a knee injury. He was scheduled to return from that late last year but a stomach virus then kept him off the court and forced him to miss the Australian Open.
He was the 2012 Australian Open runner-up, picking up 1,200 rankings points but those evaporated when the 2013 Australian Open ended.
As a result he has 5,400 ranking points and was passed by David Ferrer for No. 4 in the rankings. Nadal hasn't been this low in the rankings since May 23, 2005, just before he won his first French Open title.
Ferrer's move to fourth allows him to match his previous career high.
Novak Djokovic, who picked up his third consecutive Australian Open title Sunday, has 12,920 points and is No. 1 in the world. He's held that spot for the last 13 weeks and 66 weeks overall. He's six weeks short of Stefan Edberg, whose 72 weeks atop the rankings is 10th most all-time.
Roger Federer, who appeared in his 10th consecutive Australian Open semifinal last week, remains second with 10,265 points while Andy Murray, the runner-up to Djokovic for the second time in three years, is No. 3 with 8,480 points. Ferrer has 6,865.
Tomas Berdych remains sixth with 4,680 points followed by No. 7 Juan Martin del Potro (4,210) and eighth-ranked Jo-Wilfried Tsonga (3,555). No. 9 Janko Tipsarevic (3,180) and 10th-ranked Richard Gasquet (2,720) complete the Top 10.
There are no ATP tournaments this week, as the tour takes a week off to allow for the first round of Davis Cup play. There are eight Davis Cup series this week, including defending champion Czech Republic playing at Switzerland and 2012 runner-up Spain traveling to Canada.