Serena Williams has withdrawn from next week's Pilot Pen tournament in New Haven with a thumb injury.
Williams still plans to return in time for the US Open
The American has not played since losing to Justine Henin in the Wimbledon quarter-finals.
But Williams still hopes to be fit for the start of the US Open, which gets under way on 27 August.
"I am frustrated and extremely disappointed that I won't be able to play at the Pilot Pen," said the world number eight.
"I tried to have a full practice, hoping that my thumb would feel better, but unfortunately, it is still not 100%.
"I am not able to play at the level that I had hoped."
Williams, 25, also struggled with injuries in 2006 but came back in January to win the Australian Open as an unseeded player.