Michael Phelps dubbed as the "greatest Olympian of all time" by the Sports Illustrated as he posed for the magazine's cover decorated by his 23 gold Olympic medals.

The 31-year-old stated that his last Olympics was that of Rio but he is still considering to enter the Olympics in Tokyo on 2020. Phelps stated in SI that it would be great if he ever get the yearning to try out the 2020 Olympics. But as of now, the Olympic swimmer do not see that possibility and currently content with his retirement.

"I could probably go four more years. But could I put in the true, honest hard work? Probably. But I have so many other things going," Phelps said. "And there's no reason. I'm tapping out. I'm closing. I'm done."

His announcement of his Rio retirement is the second time he declared that he was done with the sport. He first retired in 2012 but then announced that he will be having a comeback in April of 2014. He then accumulated gold Olympic medals representing his country. According to USA Today, the swimmer appears to be determined in his decision to retire for the sport this time around.

"The hardest thing is going to be not having the chance to represent my country," Phelps said. "Not having the chance to stand on the medal platform and hear the national anthem. I'm at peace with how things ended. I'd rather have a healthy body in 20 years than kill myself more now. To me, it's a no-brainer."

Under Armour CEO Kevin Plank stated that he is hopeful for Phelps' participation for the 2020 Olympics in Tokyo. "He said he was retiring after London, when he was 27, with the lung capacity of a Great White Shark. You can bet I'm going to be nudging him as best I can for the next four years. I think he believes he is retired now. Three years is a long time to rest," Plank said.

Phelps's wife, Nicole, gave one reason that could give Phelps to come back for the sport. "I see that being the only thing that could bring him back -- to swim for, our son, Boomer," Nicole said.

"Eight years down the road, I would be so far removed that it's almost impossible to come back, physically. Unless I trained for a full four years, and that's not happening, so, to end this conversation, I'm done," Phelps stated in the magazine.