efe-epaIndian Wells, California

Rafael Nadal has withdrawn from the BNP Paribas Open ahead of his much-anticipated semi-final match Saturday against arch-rival Roger Federer, citing a right-knee injury that clearly bothered him in the previous round.

"@RafaelNadal has withdrawn from the tournament due to a right knee injury. We wish Rafa a speedy recovery. Roger Federer advances to the final by walkover.#BNPPO19," tournament organizers said on Twitter.

"I warmed up today and I felt that my knee was not good to compete at the level I needed to compete in semifinals," the Spanish great said in a news conference Saturday at this hard-court event in Indian Wells, California.

Nadal was in evident discomfort during his quarter-final match on Friday against Russia's Karen Khachanov but dug deep to pull out a 7-6 (7-2), 7-6 (7-2) victory. The world No. 2 took a medical timeout early in the second set of that contest.

The fourth-ranked Federer, meanwhile, has followed up his title earlier this month in Dubai by cruising through the draw in the California desert, not having dropped a single set and losing his serve just once in four matches.

On Friday, he cruised to a 6-4, 6-4 victory over Poland's Hubert Hurkacz in one hour and 13 minutes.

Saturday's match would have been the 39th between the two all-time greats and their ninth consecutive contest on hard courts.

Although the Spaniard enjoys a 23-15 career edge, Federer has won the last five matches.

The arch-rivals are the greatest men's tennis champions in terms of Grand Slam titles, with the 37-year-old Federer having won a record 20 and the 32-year-old Nadal having captured 17.

The Swiss great will now seek a record sixth Indian Wells title when he takes on either Canadian world No. 14 Milos Raonic or eighth-ranked Austrian Dominic Thiem in Sunday's final.

The BNP Paribas Open is among a group of nine annual men's tennis tournaments that rank just below the four Grand Slams and the year-end championship in terms of ranking points and prestige.

The top women's players also have been in action over the past week and a half at this event.

In Sunday's final, German three-time Grand Slam champion Angelique Kerber, the world No. 8, will take on fast-rising Canadian teenager Bianca Andreescu, who is ranked No. 60 and entered the tournament as a wildcard.