It doesn't take a historian to see that American men's tennis is in a poor state.

For the first time in 101 years, no American male reached the semifinals at this year's Wimbledon. It's been one decade since the last Grand Slam victory by a man from the United States -- Andy Roddick's 2003 win at the U.S. Open.

Now there's another indication of this downward spiral, and this one may be the worst.

With No. 20 John Isner's loss this week in the first round of the Rogers Cup he will surely drop a few spots in the next ATP rankings. And when that happens, it will be the first time in four decades that no American male is in the ATP top 20.

According to the ATP, at least one American has been ranked in the top 20 since the rankings started on Aug. 23, 1973.

Andre Agassi, Pete Sampras and Andy Roddick were consistently in the ATP top 10 over the past 20 years, but Roddick's retirement last year spelled doom for American males. Mardy Fish, another top American, has been sidelined by a slew of injuries recently. Fish, 31, underwent a medical procedure last year to fix an irregular heartbeat.

A problem for American men, according to some, has been a lack of athleticism. As the sport's three main surfaces become similar and technology allows for superior racquets, Americans are struggling against more athletic opponents.

Some have suggested encouraging more American youngsters to practice on clay rather than hard courts.

"Clay is where you learn how to move—you can't cheat on clay," Mats Wilander, a former No. 1 and three-time French Open champion, told the Wall Street Journal in 2011. "On hard courts, you inevitably get lazy. There isn't that big of a difference between Mardy Fish and Novak Djokovic in terms of hitting the ball, but Djokovic moves 10 times better."

As Chris Chase of USA Today points out, things don't look to be getting much better for Americans. There are only two Americans under the age of 25 who are in the ATP top 100, and they are Jack Sock (age 20, ranked 90th) and Steve Johnson (age 23, ranked 100).