The greatest clay court tennis player in the history of the open era is calling it a career this month.

Spaniard Rafael Nadal, 38, revealed last month that he is retiring from tennis after this month's Davis Cup concludes.

Read more: Rafael Nadal Retiring From Tennis

Both of Nadal's greatest rivals, 24-time Grand Slam winner Novak Djokovic of Serbia and 20-time Grand Slam winner Roger Federer of Switzerland, have now weighed in with lengthy tributes to their longtime on-court nemesis, and longtime off-court friend.

Read more: Tennis Superstar Novak Djokovic Reacts to Rafael Nadal's Retirement

While Djokovic reacted quickly to Nadal's decision, Federer waited a bit. He finally took to his social media platforms to celebrate Nadal with a touching tribute this week, ahead of what could wind up being Nadal's final match ever.

Nadal is suiting up for his native Spain this month in Malaga. Team captain David Ferrer picked Nadal to rep the country in their country's quarterfinal clash on Tuesday.

The 22-time Grand Slam champion lost in straight sets, 6-4, 6-4, to the No. 80-ranked player in the world, Botic van de Zandschulp of the Netherlands.