NEW YORK -- Neither Serena Williams nor Caroline Wozniacki rushed to the defense of Maria Sharapova, who on Monday announced she failed a drug test at the Australian Open.

"I think any time we take any medication, we double- and triple- and quadruple-check, because sometimes even things like cough drops and nasal sprays can be on the [banned] list," Wozniacki said Tuesday at a news conference ahead of her Madison Square Garden match with Serena Williams. "As athletes we really always make sure there's nothing in it that is prohibited."

Caroline Wozniacki says that athletes have to quadruple-check what they're putting into their bodies. AP Photo/Kathy Willens

Sharapova, 28, a five-time Grand Slam champion and former No. 1, claims she neglected to read the updated list of banned substances sent by anti-doping officials in December. Sharapova now faces a lengthy, potentially career-ending suspension along with an incalculable loss of prestige and income after testing positive for meldonium.

"Most people were surprised and shocked by Maria, but at the same time, most people were happy she was up front and honest," Williams said. "It showed a lot of courage about what she had done. ... That being said, it's just about taking responsibility, which she admitted she's willing to do."

Sharapova said she has been using meldonium for health reasons since 2006. The drug is of Latvian origin and not approved by the Food and Drug Administration for use in the U.S. It was put on the list of banned substances for 2016 after a lengthy study determined it was frequently and successfully used as a performance-enhancing drug by elite athletes, many from Russia and eastern Europe.

When Williams was asked whether she resented competing against a doper for a decade, Williams somewhat cryptically replied: "I'm probably not the best person to ask that question."

And when asked about speed in which clothing and shoe company Nike (which has contracts with both Sharapova and Williams) suspended its relationship with the Russian star, Williams dismissed the question, saying, "I can't comment anything on that."

Williams is 19-2 lifetime against Sharapova, which includes an 18-match winning streak dating back to 2005.