Great Olympians Who May Not Return to Compete at 2020 Tokyo Games

— -- The 2016 Summer Olympics in Rio de Janeiro officially end Sunday, and while some athletes will soon begin preparing for the 2020 Olympics in Tokyo, that is not true for all.

Here are some of the great and notable athletes who may not return for another Olympics.

Gabby Douglas

U.S. gymnast Gabby Douglas stole the show at the 2012 London games, becoming the first American to ever win gold in both the team and individual all-around at the same Olympics. But, Douglas' experience in Rio de Janeiro didn't go as smoothly. She first failed to qualify for the individual all-around competition and then finished seventh overall in the uneven bars final.

The 20-year-old was also criticized on social media for not placing her hand over her heart during the playing of the U.S. national anthem and later for appearing to not support teammates Simon Biles and Aly Raisman during their all-around final events.

"I have no regrets coming back for a second Olympic team," she said after the uneven bars final. "It's been an amazing experience. It's been teaching me a lot."

Douglas will walk away from Rio with a gold for the team all-around event for the second time in a row. Since gymnasts typically retire young, 20-year-old Douglas is not expected to return to the Tokyo games in 2020. But, teammate Raisman, 22, may make the trip. She told the Associated Press that she is in "even better" shape than in 2012 and that she gets "better with age.

After returning to the U.S. from Rio, Douglas will move from Columbus, Ohio to Los Angeles to be with her family, the AP reported.

Oscar Figueroa

Colombian weightlifter Oscar Figueroa made headlines after becoming the first from his country ever to win the gold medal for the 62 kilogram featherweight event.

After the first-place win, a visibly emotional Figueroa retired on the spot -- removing his shoes and walking away from the platform after taking a moment to kiss one of the weights.

Rio marked the 33-year-old's fourth Olympic games. In London in 2012, he won the silver medal in the 62 kilogram featherweight event.

Serena Williams

While tennis superstar Serena Williams hasn't publicly ruled out a trip to Tokyo in 2020, it's not inconceivable that the 34-year-old could skim what would be her fifth Olympic games.

In addition to her 19 Grand Slam titles, Williams has won the Olympics gold for the doubles competitions in 2000 in Sydney, 2008 in Beijing and 2012 in London. But, she was unable to extend her reign as Olympic singles champion after she was defeated by Ukraine's Elina Svitolina in the third round. She was also knocked out of the doubles tournament alongside sister Venus.

After losing to Svitolina, ranked 20th in the world, Williams said "at least" she was able to make it to Rio. "That was one of my goals," she said.

On Monday, tournament officials for the Western & Southern Open announced that Williams had withdrawn due to a shoulder injury. Despite these recent struggles, Williams is still ranked No. 1 in the world.

Michael Phelps

The greatest Olympian of all time was adamant that Rio would be his final games, but 31-year-old Michael Phelps made the same declaration after London in 2012, and some of his American teammates are skeptical on whether he'll be able to resist a trip to Tokyo.

With 28 Olympic medals under his belt, Phelps may feel as if he has nothing left to prove. But teammate Katie Ledecky suggested that he may not stick to his retirement plans.

“Last time was his last, this time was his last, and I get to say I was on the same team twice when he retired,” Ledecky told The Washington Post. “Maybe there will be a third time. All records are made to be broken.”

Phelps leaves Rio with five gold medals and one silver from when Singapore's 21-year-old Joseph Schooling beating him in the 100-meter butterfly.

Usain Bolt

On Sunday, the last day of the Olympics, Jamaican sprinter Usain Bolt turns 30 -- not a bad way to celebrate an additional three gold medals to add to his resume.

After Rio, Bolt has made a good case for the world to consider him the greatest track athlete of all time. He obtained the elusive "triple triple," defending the 100-meter, 200-meter and 4x100-meter relay titles he won in 2008 in Beijing and 2012 in London.

Bolt has previously insisted that Rio would be his last games, but it's not out of the realm of possibility for him to cancel his retirement. His longtime coach, Glen Mills, has told him that the older he gets, the harder he has to push himself, he said.

"My coach always says 'Usain you can always go on to the 2020 Olympics if you want,'" Bolt said. "So this is why he tells me to stop talking about retirement and just take it a year at a time."

Oksana Chusovitina

While most gymnasts retire in their late teens or early 20s, Uzbekistan's Oksana Chusovitina proved that age is just a number by competing in the vault final at age 41.

She placed seventh, second to last, but her performance was amazing considering that her 17-year-old son is older than some of the elite gymnasts she competed against.

Rio marked Chusovitina's seventh trip to the Olympic games. She won gold in Barcelona in 1992 as part of the team all-around event for the Unified Team of the former Soviet Union and silver at the 2008 Beijing games in the vault competition, representing Germany.

And, don't count Chusovitina out just yet. Last weekend, she declared that she would be back to compete in 2020 in Tokyo, at the age of 45.