Andy Murray again criticised Maria Sharapova over her failed drugs test, saying the Russian had no "valid excuse".
The International Tennis Federation has handed Sharapova a two-year ban after her failed drugs test at the Australian Open in January, a suspension the WTA star is appealing to the Court of Arbitration for Sport.
Sharapova, 29, insists she did not mean to break the rules, but Murray - who was similarly critical earlier this year - said that was no excuse.
"I don't really see that as being a valid excuse," he said on Tuesday.
"If you're taking any medication, it's your responsibility as the athlete to check and make sure what you're taking is legal.
"There can be the odd case where, if you were given something by a doctor, he tells you, 'Oh, this is, I don't know, a vitamin', and it's not, then that's different.
"But if you're taking medication, there is absolutely no reason why you shouldn't know whether it's on the banned list or not."
Murray was speaking after his 7-6 (10-8) 7-6 (7-1) win over Frenchman Nicolas Mahut in the first round at Queen's.
The world number two said his feelings about the Sharapova case had remained largely unchanged since the news broke.
"My thoughts haven't changed really from March. I obviously spoke quite a lot about it then," Murray said.
"I do feel like if you're cheating and or caught and gaining advantage on your opponents, then you obviously have to be punished for that."