Inflammation of the collar bone forces Russian to pull out
Sharapova was forced to withdraw from her second-round match against Australia's Jarmila Gajdosova in Brisbane, saying it was the "smart move" to make.
The French Open champion also pulled out of an exhibition match against Caroline Wozniacki at the end of December in Seoul because of a sore collarbone.
"That's why I had to pull out of the exhibition match I had in Korea," she said at a news conference on Tuesday.
"I had a bit of inflammation in my collarbone. My doctor in New York told me I couldn't really do much overhead training for about a week.
So to be fair, I haven't really given myself a chance to pretty much hit any serves or anything over my head. Just been practicing groundstrokes,’’ she added.
"So I just kind of ran out of time here,’’ Sharapova said.
While the season's first Grand Slam is set to start on January 14, Sharapova was not overly concerned about her preparations.
"I still have quite a bit of time to prepare for the Australian Open," she added. "I'm on the right track, been training really well, so I just don't want to jeopardise what I've gained in the off-season so far. I just have to make a smart move here,’’ the Russian said.
Sharapova said she expected to travel straight to Melbourne rather than make a late entry into the Sydney International next week.
Serena on course for No 1
Serena Williams credited a more subdued lifestyle on Tuesday for the current form which has put her on track to succeed fellow-American Chris Evert as the oldest world number one in women's tennis.
Williams, who recorded a serve of 200 kms an hour during a second-round 6-2, 6-2 win over France's Alize Cornet at the Brisbane International, is currently ranked third in the world.
However, the 31-year-old is regarded as the pre-eminent woman player at the moment after winning the Wimbledon, US and Olympic titles last year. Evert was aged 30 years 11 months when she was number one in 1985.