Underdogs to watch in Rio

Argentina won gold in 2004 and 2008, but 2016 will be a big measuring stick after their disappointing result in Copa America. With Lionel Messi seemingly out of the picture for the future of the national team, the Olympics will be a good look at the country's future heading into the 2018 World Cup.

The Brazilian team has several NBA players, including Anderson Varejao, Nene, Raulzinho Neto, and Leandro Barbosa. USA is heavily favored, but Brazil has the talent to be competitive.

Team USA is heavily favored for another gold medal, but Brazil's odds aren't too far behind as the host nation. 

Bronte's older sister, Cate, is favored to win the women's 50m and 100m freestyle for Australia. Bronte could give her sister some competition, however.

Cseh is neck-and-neck with Michael Phelps as the favorite in the men's 200m butterfly. The Hungarian certainly has a chance to unseat Phelps.

Going on age 35, Federer is well past his prime and likely looking at his final Olympics. He won the silver medal in London, and medaling this time around would be an excellent way to cap off his Olympic career.

The French team has several strong NBA players, including Tony Parker, Nic Batum, and Boris Diaw. They should remain competitive in the Games.

Usain Bolt is the favorite in the 100 meter and 200 meter sprints, but Gatlin's odds aren't far behind him. Both sprinters could be in their final Olympics.

Germany brings depth, though they're not favored to win with host country Brazil brings star power. The Germans could pull off an upset and are at least considered strong medal competitors.

Team USA is highly favored in women's soccer, but the German team has the second best odds and are considered the biggest obstacle.

French pole vaulter Renaude Lavillenie is favored to win, but Kendricks has a fighting chance. He won silver at the 2016 World Indoor Championships.

Wade Van Niekerk is the overwhelming favorite to win the men's 400 meter, but Merritt has a shot. He took home gold back in 2008 in Beijing.

Mola (Spain) is considered Alistair Brownlee's best competition in the men's triathlon.

Mitchell Larkin is the favorite to win the men's 200m backstroke, but Murphy has the second best odds.

Serena Williams is highly favored to win women's singles tennis. Muguruza has never won a Grand Slam tennis tournament at age 22, but the Spaniard is one of the best women's tennis players in Rio.

The former top men's tennis player in the world, Nadal is now a longshot behind Novak Djokovic. Nadal won gold in singles tennis back in 2008.

Portugal just finished winner the Euro Tournament. This team is a completely different squad, and not favored to finish in the top three. Earning a medal would be quite a coup for the country in what's already been a great year.

Led by Nuggets rookie Nikola Jokic, Serbia is a major sleeper to medal at the Olympics. They have the size to stack up against any team in the tournament.

While Katie Ledecky is the clear favorite in the women's 200m freestyle, Sjostrom is considered his biggest challenger. The Swede won silver in the event at the 2014 World Championships.

The Spanish team brings real star power with Ricky Rubio, Pau Gasol, Marc Gasol, and Jose Calderon. Anything less than a silver medal would be a disappointment for the squad.

Spain probably isn't a major competitor for Team USA in women's basketball, but they are a top candidate to win a medal.

Led by Usain Bolt, the Jamaicans are expected to win the 4x100 relay. However, USA could pose as their biggest threat.

Any kind of medal for Team USA in men's rugby sevens would be a huge upset to the world. The sport is in its competitive infancy in the States, but the US squad still has a chance to medal.

The Brazilian men's volleyball team is highly favored to win gold, but USA is considered by some to be their toughest competition. The US team last won gold in 2008.

Fellow countryman Long Ma is favored to win men's singles tennis for China, but Jike Zhang is perhaps his best competition.