Gustavo Kuerten says the absence of Roger Federer through injury is a major blow to tennis at the Olympic Games.
Swiss veteran Federer, a 17-time grand slam singles champion, pulled out of Rio 2016 and will not play again this year as he seeks to recover from a knee problem.
The 34-year-old, who won men's doubles gold alongside Stan Wawrinka in Beijing in 2008 and silver in the singles four years later, will be missed by former world number one Kuerten as he prepares to watch the quadrennial showpiece event in his homeland.
"It [Federer's withdrawal] is a big loss for Brazil," Kuerten told Omnisport.
"Perhaps the best tennis player ever but he is a human being. That is what the Olympics is all about. He loves to be in Brazil.
"I am sure he is feeling very weak and must have major problems otherwise he would be here. He had everything planned already. For us it is sad. For me, he is the one I miss the most from this Olympics."
A back problem saw Wawrinka on Tuesday join Federer in pulling out, while Rafael Nadal, men's singles gold medallist in China, is short of fitness and not certain to compete, despite travelling to South America.
Beaten Wimbledon finalist Milos Raonic has withdrawn due to concerns over the Zika virus, leaving world number one Novak Djokovic and reigning men's singles Olympic champion Andy Murray as firm favourites.
"I know Djokovic seems like he's from another world and every tournament he shows up at he almost gets the trophy straight away at the beginning but sport is not like that," Kuerten added.
"You have to prove yourself at the beginning, daily, and especially in a competition like the Olympics you have 63 other guys who want to give their all, are so hungry and with the same hopes as him.
"I am sure him and Murray are the big favourites but we will have to wait and see, but probably those two will show up in the final."