Williams joins Andy Murray, Rafael Nadal and Roger Federer in pulling out of the tournament.
The 2016 edition of the Rogers Cup takes place from 25 to 31 July.
Spain's David Ferrer has backed fellow countryman Rafael Nadal to win gold medal at Rio Olympics 2016.
The Serbian won a bronze medal in Beijing 2008 but has got no closer to gold since.
Now, three of the top four ranked tennis players will be absent after Andy Murray also pulled out of the tournament.
Tomas Berdych is Czech Republic's highest ranked tennis player.
Murray is a three-time Rogers Cup champion.
World number 67 wins in straight sets at Tasmajdan Stadium in Belgrade.
Tennis Australia to appoint Mark Draper as Hewitt's replacement.
Victory for Kyle Edmund over Dusan Lajovic on Sunday will see Britain progress to semi-final.
British number three defied the elements to secure his maiden Davis Cup win at Tasmajdan Stadium.
Richard was released from hospital but was left with some memory loss.
Andy Roddick who won the US Open in 2003 was the last American male tennis player to win a Grand Slam.
Andy Murray won his second Wimbledon title beating Milos Raonic in straight sets on 10 July.
Domestic success in 2016 lifts the gloom amid the changing and uncertain political landscape.
Serena Williams equalled Steffi Graf's open era record of 22 Grand Slam titles.
Andy Murray is unsure of his participation in the upcoming 2016 Davis Cup quarter-final against Serbia.
The Duchess of Cambridge was enthralled as she watched the Men's Final from the royal box.
The Brit previously won the Wimbledon crown in 2013.
Andy Murray has won one Wimbledon title and that was in 2013.
World number one wins 7-5, 6-3 to match Open Era record of 22 Grand Slam singles titles.
Roger Federer is yet to win a title in 2016.
World number two through to his 11th Grand Slam final after comfortable 6-3, 6-3, 6-3 victory.
Sixth seed is the first Canadian male ever to reach the final of a major tennis tournament.
Serena Williams created history, taking just 48 minutes to beat Elena Vesnina in the Wimbledon semi-final.
Andy Murray faces Tomas Berdych for a place in the final of Wimbledon 2016.
Roger Federer will be playing his 11th semi-final in Wimbledon history.
The Duchess revealed that the 2-year-old Prince has his own tennis racket and enjoys the sport.
Defending champion Serena through to her ninth final at SW19 after 6-2, 6-0 victory.
Fourth seed Kerber has not dropped a single set as yet in the tournament.