Perth - World number one Serena Williams dismissed concerns about her fitness for the upcoming Australian Open despite being forced to retire from her first singles match at the mixed teams Hopman Cup in Perth on Tuesday.
Williams had already missed the United States' opening Hopman Cup tie due to inflammation of her left knee, but took the court against Australian Jarmila Wolfe.
However, the American retired when trailing 7-5, 2-1, having appeared extremely restricted in her movement during the match, particularly on her left side.
It appeared to cast significant doubts over her title defence in Melbourne, where she will aim for a seventh singles title later this month.
Williams admitted she retired because she was being hampered by the knee and was unable to move around the court as she wanted.
However, the winner of 21 Grand Slams was confident it was only a minor problem and even refused to rule herself out of Thursday's Hopman Cup tie against the Czech Republic.
"I just have some inflammation that's been going away very slowly," she explained.
"It's still there, it's going away, but just needs a little more time.
"(It needs) a little rest, a little treatment.
"I've been training really hard during the off-season and really pushing myself beyond the limits, I just think a day off or two will make a world of difference."
Williams said her 2015 campaign, which saw the 34-year-old on target for a calendar Grand Slam until she was beaten by Italian Roberta Vinci in the US Open final in early September, had taken a heavy physical toll.
She barely played after the US Open, although she returned in the International Premier Tennis League in Manila last month.
Williams' coach, Patrick Mouratoglou, conceded Williams' knees were troubling her in November.
However, Williams said she remained confident of another successful Australian Open campaign.
"Speed is my strength so I definitely think I will be able to get it right for Australia," she said.
"I only think positive and I know I'll be okay.
"It's not even a bump, just a minor thing in the road and I'm gonna fly over it."
Williams said she hadn't made any decisions on further Australian Open preparations.