New York: Serena Williams, the top-ranked player in women's tennis, said on Tuesday she was shocked to hear her friend and fellow tennis star Maria Sharapova had failed a drug test, but she commended Sharapova for showing courage in taking responsibility.

"As Maria said, she's ready to take full responsibility and I think that showed a lot of courage and a lot of heart," Serena told reporters here.

Meanwhile, in London, Nick Bollettieri, the man who discovered Sharapova, said on Tuesday: "I think it would be devastating if they didn't allow her to come back."

Sharapova, 28, rocked the sporting world on Monday when she announced that she had tested positive for the banned substance Meldonium at this year's Australian Open, after failing to read an email saying it had been added to Wada's prohibited list.

She will be provisionally suspended from playing tennis and could be hit with a four-year ban.

Bollettieri spotted the Russian's potential when she arrived in Florida with her father in 1994. "It's up to the testing people. But I don't think she should be banned for life because of this. I think Maria will find a way to survive what is happening to her."

Former world No. 1 Sharapova, who won Wimbledon as a 17-year-old, said she had made a "huge mistake", saying that she had been taking the drug for 10 years to combat health problems. Meldonium was only added to the World Anti-Doping Agency's banned list on January 1.

Bollettieri, who also nurtured the likes of Andre Agassi and Monica Seles at the academy he started in Bradenton, Florida, and later sold it to IMG, said Sharapova should not be judged too harshly.

"This will be devastating for Maria," he said. "She really has been an outstanding character on and off the court for all these years.

"I'm not trying to say she's right or wrong, but she doesn't do discos, no drinking sprees, she has been an outstanding character on and off the court all these years. Maria's whole career has been one of dedication."

Sharapova has found less sympathy from former world No. 1 Caroline Wozniacki, who has suggested that the Russian only has herself to blame.

"Any time we take medication we double and triple check, because sometimes even things like nasal spray can be on the banned list," she told reporters in New York. "As athletes, we always make sure there's nothing in it that could put us in a bad situation."