Andy Murray has cast doubt on Maria Sharapova's insistence she took meldonium for health reasons and criticised his own sponsor Head for standing by the Russian.
Sharapova stunned the tennis world on Monday when she revealed she tested positive for the drug during the Australian Open in January.
The five-time grand-slam champion said she had been taking the drug since 2006 for health reasons and was unaware of its placement on the World-Anti Doping Agency's (WADA) list of prohibited substances at the start of the year.
Sharapova has been handed a provisional suspension from tennis, which starts on March 12, by the International Tennis Federation (ITF).
Yet, while Nike, TAG Heuer and Porsche have since distanced themselves from Sharapova, Head has said it will stand by the former world number one and even extend her contract.
But men's world number two Murray said: "It's not up to me to decide the punishment, but if you're taking performance enhancing drugs and you fail a drugs test, you have to get suspended
"I think taking a prescription drug that you don't necessarily need, but just because it's legal, that's wrong, clearly.
"That's wrong. If you're taking a prescription drug and you're not using it for what that drug was meant for, then you don't need it, so you're just using it for the performance enhancing benefits that drug is giving you. And I don't think that that's right.
"I read that 55 athletes have failed tests for that substance since January 1. You just don't expect high level athletes at the top of many sports to have heart conditions.
"Some people put a lot of trust in the team around them so it's hard to say what's the right thing for everyone but it's almost kind of part of her job to know everything that's going into her body and not just rely on what a doctor is saying or a physio is saying.
"You check yourself to make sure, double check to make sure, that anything that's going into your body is safe.
On Head's backing of Sharapova, he added: "I think it's a strange stance given everything that's happened the last few days. I don't really know what else to say on that, but that's not something I believe.
"I think at this stage it's important really to get hold of the facts and let things play out, like more information coming out before making a decision to extend the contract like that, in my view. I personally wouldn't have responded like that."