Roger Federer says Rafael Nadal "made the whole tennis world proud" with his "epic career" as he paid tribute ahead of his retirement at the end of the Davis Cup Finals.
The 38-year-old, a 22-time grand slam champion, is hoping to help Spain win the tournament taking place in Malaga this week, after confirming his retirement back in October.
Nadal has not played a competitive match since losing to Novak Djokovic at the Olympics in August, and it is not yet clear how big of a role he will play when Spain take on the Netherlands in the opening match of the Finals against the Netherlands.
Federer, who retired in 2022 having won 20 grand slams, was one of Nadal's great rivals, winning 16 matches and losing 24 of the pair's meetings.
"Let's start with the obvious: you beat me - a lot. More than I managed to beat you. You challenged me in ways no-one else could," an "emotional" Federer wrote on Instagram.
"On clay, it felt like I was stepping into your backyard, and you made me work harder than I ever thought I could just to hold my ground. You made me reimagine my game - even going so far as to change the size of my racquet head, hoping for any edge.
"You made me enjoy the game even more.
"Maybe not at first. After the 2004 Australian Open, I achieved the #1 ranking for the first time. 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.
"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.
"We were both at the start of our journey, and it's one we ended up taking together. Twenty years later, Rafa, I have to say: What an incredible run you've had. Including 14 French Opens - historic!
"You made Spain proud... you made the whole tennis world proud."
Federer, who won his final meeting with Nadal before his retirement at Wimbledon in 2019, paired up with the Spaniard for the last match of his career in the doubles for Europe at the Laver Cup.
"It means everything to me that you were there by my side - not as my rival but as my doubles partner. Sharing the court with you that night, and sharing those tears, will forever be one of the most special moments of my career," he added.
"Rafa, I know you're focused on the last stretch of your epic career.
"We will talk when it's done. For now, I just want to congratulate your family and team, who all played a massive role in your success.
"And I want you to know that your old friend is always cheering for you and will be cheering just as loud for everything you do next."