Nick Kyrgios has been forced to pull out of the Citi Open with a hip injury.

The Australian had been due to face compatriot James Duckworth in the second round but was replaced by lucky loser Jason Kubler after confirming his withdrawal.

Kyrgios was booed off court when he retired hurt at the Atlanta Open last week but says it is the same issue that has prompted his decision to sit out the tournament in Washington, DC.

The world number 17 is nevertheless confident that he will be ready for next week's Rogers Cup.

"It's the same left hip injury I got after a sudden movement in Atlanta last week and I haven't had enough time to be ready to play this week," Kyrgios said.

"The physio recommended a couple of days of rest, rehab and treatment. I've got ample time for it to settle down before Toronto.

"It's disappointing. I'm sure I'll be here again with another chance to play, but at this stage I can't risk aggravating the injury with Masters 1000s and the US Open coming up.

"Last year I wasn't healthy at the US Open, so I want to be right for that."