Wimbledon champion Andy Murray called Victor Troicki and Marin Cilic "unprofessional" on Friday, adding his voice to the growing debate about the sport's anti-doping rules.
Serbian Troicki had an 18-month ban imposed by the International Tennis Federation cut to 12 months by the Court of Arbitration for Sport (CAS) this week, while Cilic returned at last week's Paris Masters after his nine-month suspension for taking a banned stimulant was reduced to four by CAS.
Both players denied any wrongdoing and Troicki received impassioned support from fellow Serb, world number two Novak Djokovic, after Troicki's ban for failing to take a blood test at this year's Monte Carlo Masters.
Murray has made no secret of his belief that tennis needs to do more to avoid the kind of doping scandals seen in cycling and athletics, and had little sympathy for Troicki and Cilic.
In an interview with the BBC Murray, still recovering from back surgery that forced him to miss this week's ATP World Tour Finals, was unforgiving.
"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, I think, were unprofessional," he said.
"One of them refused to give a drugs test: we don't know exactly what was said in the room between the doping control officer and Viktor (Troicki), but the reality is that there are rules and you need to stick to what the rules are.
"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," Murray added.
"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."
Troicki blamed his ban on a doping control officer at Monte Carlo who, he said, told him that as the player felt unwell he did not need to give a blood test.
The Davis Cup winner returned the next day to give a blood sample that was clear and also provided a clean urine sample.
Cilic was suspended for taking the banned stimulant Nikethamide, apparently after his mother went to a pharmacy in Monte Carlo to buy glucose powder because he had run out of his usual supply.
"I personally would never go and buy something over the counter in a pharmacy. It's just unprofessional," Murray said of the Cilic case.
"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'. Look, we can't do that, you have to accept it."
Earlier this week Djokovic said he no longer trusted the anti-doping procedures in tennis, describing Troicki's ban as the result of negligence by the doping control officer who was with the player at the Monte Carlo event.
However, 17-times grand slam champion Roger Federer said Troicki had only himself to blame.
"I do believe that when you are requested for a sample, you have to give the sample," Federer said at the ATP World Tour Finals on Thursday.
"I think it's just very important to give the sample when you're requested to give it because there you are in front of them and there is no way to escape anymore."