As many American tennis players get older and close to retirement, the next generation of players need to step up. On the men's side 30-year-old John Isner leads the charge for Americans on tour. On the women's side Serena Williams holds it down at number one in the world. Within the next five years, fans will be looking to see the next generation of American players thriving at the professional level. Here are the players to look out for in the years to come.

Men's Tour

Jack Sock: 

The 22-year-old is the most successful of the young American men on tour so far. Last year, Sock was mainly known for his doubles prowess as he won the Wimbledon title with Canadian Vasek Pospisil. In 2015, Jack Sock's singles game has been starting to show as he recently reached a career high of 30 in the world. He also won his 1st ATP title this year at the US Men's Clay Court Championship. He beat fellow American Sam Querrey in the final. Sock's game has a lot of upside and a great future ahead of him.

Frances Tiafoe:

17 year old Frances Tiafoe has a lot of buzz surrounding him as he tries to establish himself on the ATP world tour. Rapper and global icon Jay Z has taken notice, as he has signed the young Tiafoe to his brand Roc Nation. Tiafoe just reached a career high ranking of 271 in the world and is looking to keep moving up the ranks in the years to come. 

Jared Donaldson:

Providence, RI native Jared Donaldson is hoping to be the United States next hope. The 18 year old Donaldson is coached by American and former pro Taylor Dent. The 6'2" American took home a challenger title by taking out 4 Americans for the title. Donaldson has a good support system around him and is hoping to build on his recent good form. Around his career high #150 in the world, Donaldson's next step is to crack the top 100.

Denis Kudla:

Denis Kudla recently made headwaves during this years Wimbledon Championships as he made it to the round of 16, a rare feat for Americans in recent years. The 22 year old pro is playing the best tennis of his life. He is riding a career high singles ranking of #78 in the world into the end of the season. Before Wimbledon Kudla title winning ability as he won the Aegon Ilkley Challenger. He continued to impress as he reached the semifinals of Atlanta. At 5'11" the young American relies on his baseline game to deter opponents and is aiming to improve his consistency to make up for his lack of height.

Women's Tour

Madison Keys:

20 year old Madison Keys has a bright future ahead of her. She has the support from coach and former American pro Lindsay Davenport. The young American already has risen to a career high of #19 in the world. Keys also obtained her first career WTA singles title. With her powerful game, Keys has the ability to beat the best players in the world. If she remains level headed on a tournament to tournament basis she can do a lot of damage on tour.

Sloane Stephens:

Sloane Stephens has been in the spotlight for quite some time now. She has shown the ability to beat current world #1 Serena Williams. Known for her great play in grand slams, Stephens has struggled in the smaller events. Recently she won her maiden WTA title at Washington and has quieted concerns. Stephens has the ability to beat any player on tour and with increased consistency she can be very successful.

Taylor Townsend:

Powerful hitter Taylor Townsend provides a lot of excitement on court. Her ability to hit winners from anywhere on court is impressive. At 19 years old, the Chicago native has a lot of upside. At last years French Open, Townsend showed her ability on the big stage as she reached the round of 32. She is looking to turn around her recent struggles and get back to winning form.

CiCi Bellis:

Last year at the US Open, CiCi Bellis shocked tennis fans around the world. The 16 year old took out veteran WTA player Dominika Cibulkova. With these results at such a young age comes high expectations for the future. Not only can Bellis be a top player on the WTA tour but she also can represent Fed Cup proudly.