He hasn't played since March 24, but Roger Federer is back at No. 1

Though he’s sitting out the clay-court season for a second consecutive season, Roger Federer has reclaimed the No. 1 ranking after Rafael Nadal fell in the quarterfinals of last week's Mutua Madrid Open.

Nadal, who won the Masters 1000 event in Madrid last year, needed to defend all of his champion’s points to hang onto the ATP tour's top spot, but those hopes were cut short by a 7-5, 6-3 loss to Dominic Thiem.

The Spaniard had won a record 50 sets in a row on clay going into that match.

And so Federer will now begin his 309th career week at No. 1. His first 308 career weeks at No. 1 came in four stints: February 2, 2004 to August 17, 2008 (237 weeks); July 6, 2009 to June 6, 2010 (48 weeks); July 9 to November 4, 2012 (17 weeks); and February 19 to April 1, 2018 (6 weeks).

The Swiss will miss the French Open for the third straight year and then make his return to the tour for the grass-court season with scheduled stops in Stuttgart, Halle and, of course, Wimbledon.

WATCH: Roger Federer travels to Zambia for the first time, for his foundation:

After his quarterfinal loss to Thiem last Friday, Nadal was asked about the ranking situation.

“Talking about No. 1, of course I prefer to be No. 1 than No. 2, and No. 3 than No. 5. I have said this a million times. And I’ve lost No. 1 before. But what makes me happy is I feel fit, and I can compete with possibilities every single week. This is my final goal: to be happy. That’s what I’m working on.”

Playing just one tournament in the first three months of 2018 also hasn’t helped Nadal's ranking.

“Between Australia and Monte Carlo I played zero tournaments. This is a lot of months given away to the other players. Having said that, I think I’ve placed myself in a good position now, more or less. And I still have some good weeks on clay, and then I’ll keep on moving forward. This is the reality.”

And Nadal may not be No. 2 for long—the 16-time Grand Slam champion can take the top spot right back from Federer by winning the Masters 1000 event in Rome this week, something he’s accomplished an incredible seven times in his career (2005, 2006, 2007, 2009, 2010, 2012 and 2013).

He may also have a shot at revenge this week—Nadal, seeded No.1 in the Italian capital, could have a quarterfinal rematch against Thiem, who’s seeded No.6, should they both make it that far.

The Spaniard will play either Fernando Verdasco or Damir Dzumhur after a first-round bye.

WATCH: Rafael Nadal wins his 50th consecutive set on clay: