(CNN) -- Serena and Venus Williams may still be the players to beat on the women's circuit while Andy Roddick has enjoyed a recent renaissance on the men's tour but strip away this illustrious trio and there are real fears for the future of American tennis.
Roddick remains the only U.S. male in the top 10 of the ATP Tour rankings, with John Isner and Sam Querrey solid performers in the 20s.
On the WTA Tour, Serena and Venus are at No. 1 and No.4 but then there is a gap to promising teenager Melanie Oudin at 36, with three other women occupying spots in the lower reaches of the top 100.
For a nation with the tennis pedigree of the United States, and with its three standard bearers in their late 20s, it is a worrying trend which Roddick says is a product of the talent pool in the United States being diluted.
"I think our best athletes probably get spread out across 10 or 12 different sports," he told CNN in an exclusive interview.
"Where in Serbia -- with the success of Novak (Djokovic) and the other girls on tour and guy players too. It's kind of become the sport there.
"Their best athletes -- have been funneled into tennis. In the States -- I feel like it's funneled into football, baseball, and basketball. There are so many different options that it might water down the talent pool for a given sport," he added.
Nick Bollettieri, whose famous tennis academy has produced the likes of Andre Agassi and Maria Sharapova, agrees with Roddick.
"Look you have cheerleading, you have basketball, you have lacrosse, you have basketball, football, you have everything," he told CNN.
"You have marathons, running, we have a variety of things. I believe you have to go for one sport and dedicate your life to it and also have some talent."
Bollettieri also believes the worldwide growth of tennis with many more countries now producing top-ranked players is responsible for the relative decline in U.S. standards.
"Let's go back to the 80's and 90's. Basically there were six countries playing and we certainly we were right up on top and if you look at the world today you have China -- unbelievable ladies and India, you have Japan, the Czech Republic, you have Serbia, you have everybody playing," he said.
Bollettieri also questions the failure of U.S. tennis to discover talent at grassroots level from working class backgrounds.
"How many of the kids playing today come from poor families? How many have come from the inner city where there is a possibility they can be somebody? It is very difficult today in America to get players to commit," he added.
In response to the problem, the U.S. Tennis Association (USTA) has charged Patrick McEnroe with developing its elite young players, combining this role with captaining their Davis Cup team.
McEnroe, whose brother John topped the world rankings in the 1980s, agrees with Roddick about the attractions of other sports, but is not going to make it an excuse for failure.
"We've got to do a better job," he told CNN. "We need to find those players and train them more systematically."
He says he has been given sufficient funding and resources by the USTA, but says no amount of money can develop a grand slam winner if the talent is not there.
"I'm not sure you could create a champion. I'm not sure that's possible, but I think you can create an environment where you will get a lot of really good players, hopefully if you do that, you will get the Serena Williams, the Andy Roddicks." he added.
Pete Sampras, the last American man to top the world rankings, has no doubt the USTA made the right choice in selecting McEnroe to his role two years ago.
"Patrick is a good friend, a great Davis Cup captain and a solid ambassador for the sport of tennis. I wish him nothing but the best and will help in any way I can," he told the USTA official Web site.
Despite the support for McEnroe, the flow of young U.S. talent onto the professional circuit remains a trickle rather than the hoped for flood.
Current hopes are the Harrisons, 17-year-old Ryan and his younger brother Christian, who are both at the Bollettieri Academy.
Ryan became the third-youngest player to win an ATP Tour match at 15 and Bollettieri believes he has the talent to make it to the top from his current ranking in the mid 200s.
"He certainly has the ingredients and that is what this academy does. It provides the basis and then it is up to you and how you want to compete and if you can deal with competition," he added.
Despite the talent of the likes of the Harrisons and more established young players such as Oudin and Isner, Bollettieri does not believe that future success is guaranteed.
"Pat has got a tough job, not impossible but he is the one who is going to have to go out, get all the good coaches, support them and get the good players with the good players and work with the colleges.
"But you are still going to have to seek out the hungry athletes," he added.
In the meantime, Roddick, who scored a superb victory in the Miami Masters 100 tournament recently, is hoping that Isner and Querrey can step up to the plate to give him some support in the upper echelons of the world game.
"I've been real excited that Sam and John have been playing well. I'm certainly always welcome to have some home company in the top ten or so," he said.