Tennis great Roger Federer hailed his former rival Rafael Nadal on Tuesday ahead of the Spaniard's imminent retirement from tennis at the Davis Cup.

"Rafa, I have to say: What an incredible run you've had. Including 14 French Opens -- historic!" Federer wrote on social media platform X.

"You made Spain proud... you made the whole tennis world proud."

Retired Swiss star Federer and Nadal faced each other 14 times at Grand Slam tournaments with Nadal holding a 6-3 advantage in finals.

The Spaniard also had a 24-16 winning record overall in their 40 head-to-head meetings.

"I keep thinking about the memories we've shared... always cracking each other up," wrote Federer.

"Wearing each other out on the court and then, sometimes, almost literally having to hold each other up during trophy ceremonies."

Federer won 20 Grand Slams, a tally only beaten in the men's game by Nadal on 22 and Novak Djokovic, who holds the record at 24.

"You beat me -- a lot. More than I managed to beat you. You challenged me in ways no one else could," Federer continued.

"You made me reimagine my game—even going so far as to change the size of my racquet head, hoping for any edge."

Nadal, a 22-time Grand Slam winner, will bow out from professional tennis after competing with Spain at the Davis Cup.

David Ferrer's team face the Netherlands in the quarter-finals on Tuesday, although it is unknown if Nadal will participate in the tie.

The 38-year-old has struggled badly with injury in the last few years, leading him to the decision to retire.

- 'It wasn't just hype' -

Federer recalled Nadal partnering him in doubles at his own retirement at the Laver Cup in 2022.

"It meant everything to me that you were there by my side -- not as my rival but as my doubles partner," added Federer.

"Sharing the court with you that night, and sharing those tears, will forever be one of the most special moments of my career."

The pair met for the first time in 2004 at the Miami Open, shortly after Federer had become world number one and Nadal was just 17.

"I thought I was on top of the world. And I was -- until two months later, when you walked on the court in Miami in your red sleeveless shirt, showing off those biceps, and you beat me convincingly," said the 43-year-old.

"All that buzz I'd been hearing about you — about this amazing young player from Mallorca, a generational talent, probably going to win a major someday - it wasn't just hype."

Nadal said Monday he was not at the Davis Cup to retire but to try and win it with his country.

However he has not competed in an official singles match since his second-round exit at the Olympics in July.

"I am not here for retiring. I'm here to try to help the team," Nadal explained.

"It's of course going to be my last week on the professional tour, but at the end, we are here in a teams competition.

"The emotions are going to be for the end."