London - Wimbledon champion Andy Murray on Friday blasted Viktor Troicki and Marin Cilic as "unprofessional" after both were handed doping bans with the British star backing the drug testing system.
Troicki is serving a 12-month ban for failing to supply a blood sample on demand at the Monte Carlo Masters in April when he claimed he was too ill.
Cilic served a four-month suspension after testing for banned stimulant nikethamide at the Munich Open in May.
Croatian star Cilic, who returned to action in Paris last week, said the substance was in a supplement bought by his mother from a chemist in Monte Carlo.
But Murray believes there can be no excuses when it comes to trying to explain away offences.
"Whether either player was intentionally cheating or not - we don't know that, and I don't think either of them are like that - but both of them were unprofessional," Murray told the BBC.
"I personally would never go and buy something over the counter in a pharmacy - it's just unprofessional.
"I think 10 or 15 years ago, when people didn't think drug taking happened in sport, people might have thought 'yeah, we can just buy stuff over the counter in any old pharmacy'. But we can't do that and you have to accept that."
Troicki was originally banned for 18 months before his punishment was reduced this week after the Court of Arbitration for Sport decided that "his fault was not significant".
The 27-year-old Serb insisted that a doping control officer told him he could return the following day in Monte Carlo to take the blood test, something the officer denied.
He did give a blood sample 24 hours later and it showed no irregularities.
"We don't know exactly what was said in the room between the doping control officer and Viktor but the reality is that there are rules and you need to stick to them," added Murray.
"When we're asked to go and give a drugs test, we must do that.
"I'm happy that the drug testing is going in the right direction: they're starting to increase it, they're doing more blood testing and we've got the biological passports in place.
"There almost has to be zero tolerance on that stuff because, if not, people are just going to think they can get away with anything."
Earlier this week, 17-time Grand Slam title winner Roger Federer called for more drug tests in tennis.
"I just feel like we're not getting maybe tested enough," said Federer.
"I didn't get tested in Basel, in Paris (October). I got tested here (at the ATP World Tour Finals in London) after the first match.
"I feel like I used to get tested more, I think I was tested 25 times in 2003, 2004. Ever since, I think it's been clearly going down this season."
Federer spoke after outrage from world number two Novak Djokovic over the ban handed to his fellow Serb Troicki.
Djokovic said he no longer trusts the anti-doping system.
"It proves that this system does not work," said the Serb.
"First of all, he's not positive on any banned substance. I'm not saying that it's completely not his fault.
"She (the DCO) did not clearly present him all the severe consequences that he will have if he avoids that. She told him that he needs to write a report and that he will be just fine.
"And because of her negligence and because of her unprofessionalism, he is now off the tour for one year. And now it makes me nervous as a player to do any kind of test.
"I don't have trust in them anymore. I don't have trust in what's going on."