Federer, the winner of 17 Grand Slam singles titles, is now ranked No. 5. He says in a statement he's "disappointed" to miss the Montreal event and looks forward to playing there again. He won the Rogers Cup in Toronto in 2004 and 2006.
Federer lost to No. 55 Daniel Brands last week in his opening match at the Swiss Open. In Hamburg, Germany, he cited back pain in his defeat to No. 114 Federico Delbonis. He fell to No. 116 Sergiy Stakhovsky in the second round at Wimbledon.
Ivan Dodig of Croatia and Pablo Andujar of Spain will join the main draw in Montreal. Viktor Troicki and Marin Cilic also will not compete, joining Jo-Wilfried Tsonga and Mardy Fish on the sideline.