Nick Kyrgios has spoken on fellow countryman Max Purcell's recent ban.
Purcell, a former doubles grand slam champion, was hit with an 18-month suspension on Tuesday after he was found to have breached the Tennis Anti-Doping Programme (TADP).
The 27-year-old admitted to using a prohibited method to receive intravenous infusions.
Having already served a chunk of his penalty, Purcell will be permitted to return to tennis in June 2026.
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Kyrgios has questioned the length of the ban.
"So honest feelings about how ridiculous Purcell’s ban is? Vitamins? Can we justify this?" he wrote on X.
"Or can we just admit now that the whole system is cooked [laughing emoji]."
Earlier this year, Kyrgios was critical of the three-month ban handed to men's world No. 1 Jannik Sinner.
He criticised the "fairness" of the suspension following the Italian's two positive drug tests in 2024.
Sinner had previously been cleared of any wrongdoing by an independent panel after testing positive for the banned substance clostebol.
The World Anti-Doping Agency (WADA) sought a ban of up to two years before accepting the three-time grand slam champion "did not intend to cheat".
"So WADA come out and say it would be a 1-2 year ban. Obviously Sinner's team have done everything in their power to just go ahead and take a 3-month ban, no titles lost, no prize money lost," Kyrgios wrote on X in February.
"Guilty or not? Sad day for tennis. Fairness in tennis does not exist."