Trainer Gerard Butler could face a ban from racing after admitting to injecting horses with anabolic steroids.
Butler told the Independent he had made an "unpardonable misjudgement", and comes just days after fellow Newmarket handler Mahmood Al Zarooni was banned for eight years after he admitted to administering anabolic steroids to 15 horses in his care.
The trainer has already informed the British Horseracing Authority that several of his horses had been treated, on veterinary advice, for injured joints with a banned substance.
Butler told the Independent: "I have been totally candid throughout, and it was I who told the BHA that I had treated four colts in December and January.
"I'm not trying to defend myself, just to explain what happened. And I must emphasise I was advised in good faith by my vets.
"It was an unpardonable misjudgement, purely to cut corners in what is a very expensive treatment.
"I have been very uncomfortable over the past few days, hearing and reading about the Al Zarooni case.
"I feel people need to know about what has happened in my yard."
Butler believes 'Sungate', the medication in question he used on veterinary advice to treat horses' joints, has been "misunderstood by many others".
He said: "I know I'm obliged to satisfy myself that each and every treatment is within the rules, and I failed to do so in this case.
"But I am certain that this medication has been misunderstood by many others.
"And I just hope that the BHA is being suitably rigorous in establishing whether that is indeed the case.
"It did not cross my mind that there could be any problem with this medication.
"And, judging from the fact that the BHA said nothing about it when they saw my medical book, it does not seem to have crossed their minds, either.
"Little Black Book ran on August 4, and won a couple of weeks later, so they would have known he was clearly in training at the time.
"In the medical book, I signed that I had authorised use of the drug, and my vet had countersigned for its administration.
"Sungate had for some time been widely used in their practice, with very beneficial results for joint injuries."
Godolphin are in "no rush" to appoint a new trainer at Moulton Paddocks in Newmarket.
The British Horseracing Authority said last week Godolphin have around 10 days to find a replacement for Al Zarooni if Moulton is to remain active as a licensed training stable this season.
But Godolphin racing manager Simon Crisford said the most pressing issue is to ensure the yard is "clean of drugs".
He told the Telegraph: "Sheikh Mohammed has ordered a lockdown at Moulton Paddocks and it doesn't matter if those horses don't race again this season.
"His priority is to see that it is clean of drugs. The testing will take place this week.
"There is no rush to appoint anybody to train there at present.
"As far as we could see, the yard became inoperative when Mahmood Al Zarooni was banned and his licence was cancelled.
"What Sheikh Mohammed has stressed to me is the need to clean up this mess as quickly as possible."