Venus Williams joined sister Serena in withdrawing from the US Open as the final Grand Slam of the year lost another two high-profile players.
Serena, 39, wrote in a social media post on Tuesday that she needed time to allow her body to "heal completely" from a torn hamstring.
The 41-year-old Venus then withdrew hours later with a leg injury.
It will be the first time since 2003 that neither Williams sister has appeared at Flushing Meadows.
The tournament, which begins on 30 August, will also be missing defending men's champion Dominic Thiem, Roger Federer and Rafael Nadal.