Tennis legend Andre Agassi believes there are two American players from the younger generation who can succeed the pair of Roger Federer and Rafael Nadal.

Despite being in their thirties, Federer and Nadal are still dominating the sport, particularly since the beginning of last year where they both shared the four Grand Slams and won a combined 13 titles in 2017.

Federer went on to win his 20th Grand Slam at the 2018 Australian Open and is the overwhelming favorite to win a ninth Wimbledon crown in July. Nadal, meanwhile, won his 11th French Open title Sunday and already boasts four titles in 2018.

The duo's recent dominance has led to continued debates as to why the current generation have failed to challenge them, especially when considering the fact that along with Novak Djokovic, who has 12 Grand Slams, the trio all won their first major titles before the age of 22.

Whenever their time at the top of the sport does comes to an end though, Agassi believes the likes of Frances Tiafoe and Reilly Opelka, both 20 years old, can take over.

Frances Tiafoe Frances Tiafoe of the United States is regarded as one of the brightest prospects in tennis. Here, Tiafoe plays a backhand during the men's singles first round match against Sam Querry of the United States during day two of the 2018 French Open at Roland Garros in Paris, May 28, 2018. Photo: Matthew Stockman/Getty Images

"You look at the next generation, the top two leading the pack as far as potential, Frances Tiafoe who I think is a hell of an athlete," Agassi was quoted as saying by Express. "I think he can bring a lot to the table and possibly put himself in position to be a factor at Slams in the upcoming years."

"Then you look at something you can’t teach like Reilly Opelka, who is 7ft tall.  I mean it’s slim pickings when you talk about the best in the world and you better bring something that’s very unique, you’re competing against the world. But this is probably one of the most optimistic generations that we have now of having somebody stick through."

Tiafoe has a Delray Beach title to his name from earlier in the year and is currently ranked 63rd in the world, though he did reach a career-high 56 in April. Opelka, meanwhile, is the tallest player on the tour and is a junior Wimbledon champion, currently ranked 153rd in the world.

Reilly Opelka Reilly Opelka most recently took part in the French Open. Here, he serves to Taylor Fritz during the BNP Paribas Open at the Indian Wells Tennis Garden in Indian Wells, California, on March 8, 2018. Photo: Matthew Stockman/Getty Images

Coincidentally, Federer praised Tiafoe last year after defeating him at the Miami Open.

"I've hit with Frances maybe twice before: Once at the French and once at the U.S. Open. There he surprised me," Federer said at the time. "I'm not going to get the surprise really a second time around because I saw the power he had, the explosivity he had."

"So I think he's going to be really good, like most of the NextGen campaign, if you like, are going to be good players."

Federer is set to return to competitive action for the first time since March at the Mercedes Cup in Stuttgart, Germany, on Wednesday. The Swiss legend takes on Mischa Zverev in a round of 16 clash.