Russian tennis player Maria Sharapova signs a poster before launching a TAG Heuer watch in New York, United States, in this August 22, 2006 file photo.[Photo/Agencies]

"I'm extremely angry and disappointed. I had to lose my career and never opted to cheat no matter what," tweeted former world No. 1 Jennifer Capriati, in a long series of posts attacking Sharapova.

Aries Merritt, a U.S. hurdler, said there was no excuse for Sharapova to be unaware that WADA added meldonium to its latest list of banned drugs effective Jan. 1, which it circulated to competitors.

"As an athlete it is your responsibility to always know what's being placed on the banned list. Period," said Merritt at the U.S. Olympic Committee summit in Los Angeles.

Former U.S. Olympic swimmer Aaron Peirsol told Reuters there was some confusion over meldonium. "It wasn't even anything that was illegal until the beginning of this year," he said. "You have a bunch of people taking stuff that the athletes probably don't even know (is illegal)... it becomes gray."

Sharapova said she had not read an email informing her that meldonium was banned for use in sport.

She will be provisionally suspended from playing tennis from March 12 and could be prevented from competing for Russia at the Rio de Janeiro Olympics this year.

SOME SPONSORS ON THE FENCE

Tennis player Maria Sharapova of Russia poses next to a Porsche at the Grand Palais in Paris, France, in this May 21, 2015 file photo. [Photo/Agencies]

Sharapova's deal with Tag Heuer, owned by French luxury goods group LVMH, expired at the end of 2015, and the company said on Tuesday it had dropped renewal talks in view of her announcement.

Nike Inc, the world's biggest sportswear brand, and German luxury car maker Porsche, a unit of Volkswagen AG , have said they are suspending their relationship with Sharapova as they gather more information and wait for a decision on a ban.

A person close to Sharapova told Reuters her team was encouraged that none of the sponsors so far have said they were terminating contracts with the player, although they had the right to do so.

"Suspension means to put on hold," the source said, requesting anonymity because of the sensitive nature of the situation. "Under the circumstances we're very pleased that everybody is willing to stand by and see what facts come out instead of terminating."

Danone SA, the maker of Evian water, a longtime Sharapova sponsor, said on Tuesday it would monitor developments. Avon Products Inc, another sponsor, declined to comment on its endorsements.

Brian Socolow, an expert in sports law and a partner at Loeb & Loeb LLP, said Nike's quick suspension was no surprise after its long support for now-disgraced U.S. cyclist Lance Armstrong.

But he said Sharapova may yet win back sponsors. "She has the chance, like other athletes, to redeem herself and regain her leadership position as an endorser," said Socolow. "She will have to demonstrate that it was an honest mistake and there are no other improper reasons she took the drug."

There was some scepticism about the sponsors' motives from tennis fans on social media.

Ben Stanley (@BDStanley) tweeted on Tuesday, "Nike is in the business of making money, not offering moral guidance. If it paid to keep Sharapova on, they'd do it."

(Additional reporting by Lidia Kelly in Moscow, Ilona Wissenbach in Frankfurt, Michael Shields in Zurich, Gina Cherelus and Anjali Athavaley in New York, Steve Keating in Los Angeles and Ben Klayman in Detroit; Writing by Bill Rigby; Editing by Timothy Heritage and Tiffany Wu)