A back injury forced Lleyton Hewitt to withdraw from the Sony Ericsson Open on Friday shortly before his scheduled second-round match against Dutchman Raemon Sluiter.
The Australian former world number one suffered with the problem during a loss in the second round at the Pacific Life Open against Serb Janko Tipsarevic less than a fortnight ago.
"I'm disappointed but my back has not come up as well as I would have liked from last week, which is frustrating for me," he told reporters.
The 19th-ranked Hewitt, who won the Las Vegas title this month, said he had withdrawn to reduce the chance of further injury.
"That's the last thing I need at the moment. I don't want to go on the court knowing that I can't compete at my best."
Hewitt, who had been given a bye into the second round, was replaced in the draw by American Robert Kendrick.
