Cape Town - World No 1 Serena Williams has become the latest high-profile player to pull out of the Rogers Cup, which gets underway on Monday.
Williams, who has won the tournament three times in the past, cited inflammation in her shoulder as the reason for her withdrawal.
With the Olympic Games fast approaching, Williams does not want to take any risks that will jeopardise her chances of representing the United States in Rio de Janeiro.
"Due to inflammation in my shoulder, I unfortunately must withdraw from the Rogers Cup," Williams said in a statement. "I was looking forward to competing in Montreal and I look forward to returning soon."
Williams, who recently equalled Steffi Graf’s record of 22 grand slam titles after winning Wimbledon earlier this month, joins reigning men’s singles champion Andy Murray, Roger Federer and Rafael Nadal in missing the event.
Rogers Cup director Eugene Lapierre was disappointed that Williams had withdrawn, but fully understood her decision to do so.
"Of course, we are disappointed that Serena will not play in the tournament this year," he said in a statement.
"Because this is an Olympic year, the players have very full schedules. Sometimes your body needs rest. We hope that Serena will recover quickly and wish her much success for the rest of the season."