Andy Murray has pulled out of next week's Pilot Pen event in New Haven as he struggles to fully overcome a serious wrist injury.
Murray is still hopeful of being fit for the US Open
The British number one returned after three months out last week but has lost two of three matches since.
He suffered a 6-1 6-2 loss to Marcos Baghdatis in Cincinnati on Tuesday.
A statement on Murray's website said: "He isn't ready to play. Instead, he'll keep working hard and hopes to be ready for the US Open."
The 20-year-old Scot has been unwilling to hit his forehand at full power since returning in Washington last week, but said after his defeat by Baghdatis: "I haven't had any bad reactions.
"It was feeling better, and I guess it's pretty much 100% now. It's a good sign."
The US Open gets under way on 27 August.