Seven-time singles Grand Slam champion Venus Williams crashed out of the Chicago Women's Open in the first round after being handed a wildcard.
It comes after her world ranking dropped to 147, her lowest since 1997.
The oldest person in the draw at 41, former world number one Williams lost 6-2 6-3 to Taiwan's Hsieh Su-wei.
Elsewhere at the WTA 250 tournament, Great Britain's Heather Watson retired hurt while 6-2 1-0 down against Romania's Ana Bogdan.
At the Cleveland Championships, GB's Tara Moore was beaten 6-4 7-5 by Linda Fruhvirtova in the first round.
US Open qualifying starts on Tuesday, with seven British players hoping to join Johanna Konta, Watson, Dan Evans, Cameron Norrie and Andy Murray in the main draw.
Williams has been awarded a wildcard for the Grand Slam - at which she won the singles title in 2000 and 2001.
The US Open takes place from 30 August-12 September.