Andy Roddick's slide from ninth place on the ATP list means that US players will be missing on Monday from the elite rankings for the first time ever,dpa reported.
As the Toronto Masters begins, Roddick will have fallen from the top 10 due to a third-round defeat at the Legg Mason event in Washington to Frenchman Gilles Simon.
Since the ranking system began in 1973, at least one US player has always figured in the top 10 - a span of almost four decades. When the list began, Americans dominated the sport in the era of Jimmy Connors and Arthur Ashe. Roddick's exit leaves the former power now a footnote.
Roddick made what he had hoped was a breakthrough by winning the Miami hard-court title in April, but since then has had little to show on court. The last local to win the US Open (2003), Roddick lost in the Wimbledon fourth round.
He was considering a health check-up during the run-up to Canada, with his participation in Toronto reportedly in doubt.
"I haven't been feeling quite right. I haven't been feeling well for some weeks. I feel pretty lethargic and not quite as excitable as I normally am," Roddick said. "Something doesn't feel quite right. Maybe it could be a vitamin deficiency. We will have to take a look at that."
The next highest Americans are John Isner at 19th and number 20 Sam Querrey, among the six US players in the top 100.