Agnieszka Radwanska said she was "shocked, like everyone else" when Maria Sharapova revealed Monday that she failed a drug test in January at the Australian Open.

"It was a very sad day for tennis, that's for sure," Radwanska said Wednesday at BNP Paribas Open at The Indian Wells Tennis Garden.

Petra Kvitova and Simona Halep used much the same words while discussing Sharapova's positive test for the drug Meldonium.

Sharapova said she had been taking the drug since 2006 to help deal with a magnesium deficiency and other health issues, but wasn't aware the World Anti-Doping Agency had added it to the list of prohibited substances this year because she hadn't looked at the updated list.

Halep, the defending women's champion in the Indian Wells event that started Wednesday, called it "a tough moment for the sport, a bit disappointing," and Kvitova said "I hope it will not affect the tennis world. I hope that the fans will still like tennis."

Men's star Rafael Nadal termed it "terrible for the world of sport in general and for our sport especially."

"It's terrible because the sport must be clean and must look clean," Nadal said. "We have a good anti-doping program and the players who are not doing the right things are going on trial, so we will see how it goes."

Nadal said he lets his doctor keep track of the changes on the prohibited substance list and is "100 percent confident with my team" and knows everything he is taking. But he also knows that nothing is foolproof.

"It's difficult to imagine that something like this can happen, but there's always mistakes. Everybody can have mistakes. I want to believe that for sure it's a mistake for Maria, she didn't want to do it, but there's always (the possibility) that it's negligence.

"The rules are like this and now she must pay for it."

Halep said she personally checks the WADA update each year and "always when I take something I turn to the people that are taking care of this, the anti-doping, and everything is sure. If you take something you have to check very carefully before."

Kvitova, a two-time Wimbledon champion, said: "I think it's something which we all should know, what we are taking and what we are putting into the body," and thinks Sharapova made "a huge mistake."

Radwanska called it a mistake as well, but she can understand how it happened.

"I'm scared because I know every pill can have something (prohibited) in it," said Radwanska, who said she has been tested three times this year. "So when I'm sick I'm just taking aspirin because I'm always afraid there's going to be something else in it (medication). "

Kvitova said in one way the incident can be a positive for the sport because "I think this is the kind of example that we see that they are trying to have a clean sport. I think the system is working and they are doing a good job."

What none of them knows or would even speculate on is what penalty Sharapova might face. The International Tennis Federation's anti-doping program regulations recommend a four-year ban if the violation was intentional and a two-year ban if it was accidental.

"For sure it's a sad day for tennis but what can I say more? We're all waiting for what they're going to do about it and that's it," Radwanska said. "I don't know. I have no idea what they going to do."