Australian Open doubts for Maria Sharapova Maria Sharapova, the world No 2, insists her Australian Open plans are still on track even though she has had to pull out of her chosen warm-up event with an injury to her collarbone. Sharapova dropped out of the Brisbane International while practising for her opening match. Eight of the world's top 10 women have entered the tournament. The injury, to her right collarbone, also forced her to pull out of an exhibition match in South Korea last week. But she insists she will be fit for the Australian Open, which starts on 14 January, and said that her latest injury was "not at all" related to the shoulder problem that has plagued her since 2008. I still have quite a bit of time to prepare for Australia. 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," Sharapova said. Just have to make a smart move here. It's kind of the way that I've always built my career, around the fact that it's very important for me to go into something like the Australian Open believing and knowing that I'm healthy, that I'm confident. I don't exactly need to play five tournaments in order to feel that way. Sharapova, the reigning French Open champion, also pulled out of the Brisbane International last year, but still managed to get to the final of the Australian Open, where she lost in straight sets to Victoria Azarenka. She added: "I had a bit of inflammation in my collarbone, and I sent [scan results] to a doctor in New York and he 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 ... So I just kind of ran out of time here. Laura Robson's run in the Shenzhen Open ended at the second-round stage yesterday, with the Briton losing in straight sets to Monica Niculescu. Robson was barely in the match against the Romanian, losing 6-2, 6-3 as she failed to live up to her seventh seeding. The world No 53 will now spend the remainder of the week fine-tuning her preparations for the Australian Open. Serena Williams is aiming to surpass Chris Evert as the oldest world No 1. Evert was 30 years and 11 months old when she topped the rankings in 1985. Williams, 31, is currently world No 3.