Federer, who spent more weeks at No. 1 than anyone, already had reached his lowest spot in a decade by dropping to No. 5 after Wimbledon – and he fell two more places Monday.
Barring a withdrawal, Federer will be seeded seventh at the U.S. Open, where he won five of his 17 Grand Slam titles.
In other changes, French Open champion Rafael Nadal – who won hard-court titles at Montreal and Cincinnati the last two weeks – rose to No. 2 from No. 3, swapping places with Wimbledon champion Andy Murray. Novak