I hope every one in here who makes a drug accusation towards a player without valid proof gets a infraction like I did.
You can make it in a way that you don't directly point at a specific player.
Like, Let's suppose player X had breathing and allergies problems and withdrew from several matches early in his career then to turn into one of the fittest on tour being able to contest back to back 5 set matches like it's nothing. Wouldn't that sound strange?!
If you want to be more obvious you could say: Maybe gluten-free diet could be the reason for the hypothetical case