Six-times champion Roger Federer canceled his practice session at the ATP Finals on Monday, the day after losing his opening round-robin match to Kei Nishikori at the O2 Arena.
Federer, making his 16th appearance at the ATP's showpiece finale, had not lost any of his previous 45 round-robin matches in straight sets before his 7-6(4) 6-3 loss to the Japanese player.
It means the 37-year-old faces an uphill battle to reach the semi-finals for the 15th time and another straight sets defeat by Austria's Dominic Thiem on Tuesday could prove terminal.
After his defeat on Sunday, Federer spoke of the difficulty he has had trying to find a practice court that matches the speed of the fast indoor showcourt at the O2 Arena.
"It's just that practice has been a bit all over the place," he told reporters. "Practised in Queen's (Club), practised on the outside courts here, then center as well.
"So it's not always exactly the same conditions."
Last month, 20-time Grand Slam champion Federer revealed that he has been struggling with a hand injury since this year's grasscourt season.
"I hurt my hand training at the start of the grass season," Federer said at Basel tournament which he won.
"It's had more consequences than I thought. I dragged this pain for about three months."
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