Russian world number three Nikolay Davydenko became the fifth withdrawal through injury or illness at the Sydney International Wednesday, retiring from his second round match with a foot injury.
Davydenko called it quits after losing the first set 6-4 to Paul-Henri Mathieu. The Frenchman will face compatriot Richard Gasquet in the quarter-finals on Thursday.
Davydenko said he had a possible stress fracture in his right foot and retired as a precaution ahead of next week's Australian Open.
He said he would have scans to determine the extent of the injury before deciding whether he would play in Melbourne.
"It's important that I now go to Melbourne and have a scan because the doctor says it could be a stress fracture," Davydenko said.
"If that is the result I will pull out the Australian Open, that's why it's very important not to have the injury.
"I now have a couple days to check and see what's wrong, what's happened there, because it first happened last week playing in Doha."
Davydenko, who reached the semi-finals of last year's US Open, said he withdrew to save himself for the Australian Open, starting in Melbourne on Monday.
"Because it's a small tournament, I don't think anybody cares about playing here in the tournament," he said.
"I need to prepare, like if you go through a few matches and go to prepare for the Australian Open."
Davydenko joined Spanish world number two Rafael Nadal (thigh), Thailand's Paradorn Srichaphan (wrist), Russian women's world number four Svetlana Kuznetsova (virus) and Russian number six Nadia Petrova (abdominal).