Azarenka pulled out on Wednesday after hurting her right knee in her opening-round win against Maria Joao Koehler. She withdrew minutes before her second-round match against Flavia Pennetta.
Azarenka, the two-time Australian Open champion, had reached the semifinals at Wimbledon the last two years and had been seeded to face Serena Williams in the final.
Steve Darcis, who beat two-time champion Nadal in straight sets on Monday in one of Wimbledon's greatest upsets, pulled out because of a right shoulder injury.
The 135th-ranked Darcis was scheduled to play Lukasz Kubot of Poland.
John Isner, the 18th-seeded American, retired during his second-round match against Adrian Mannarino of France with a left knee injury after only two games.