A doctor at the centre of sports doping allegations poses "a potential future risk of harm to patients", a medical tribunal has concluded.
Dr Mark Bonar, 38, faces sanctions on his registration after it was ruled his treatment of a cancer patient amounted to serious misconduct.
In March, Dr Bonar was reported to have claimed he treated more than 150 sports people, including Premier League footballers, with banned substances such as EPO, human growth hormones and steroids.
He dismissed the Sunday Times allegations as "false and very misleading".
Since last year he has faced unrelated matters in relation to his care of an American in her 40s at a five-star Mayfair hotel apartment between December 2013 and January 2014.
Patient A received total parenteral nutrition (TPN) - a form of intravenous feeding lasting eight hours per day - in a treatment plan drawn up by Dr Bonar.
The doctor said he was forced into the "temporary arrangement'' because Patient A was unable to be treated at a private clinic because of unpaid medical bills.
Earlier this week the Medical Practitioners Tribunal Service found the doctor gave the treatment when it was dangerous to do so and that the risks associated with it were increased by inadequacies in her care.
Dr Bonar treated her without the assistance of a multi-disciplinary team or the supervision of an appropriate consultant but he was cleared of an allegation he failed to tell Patient A her condition was terminal.
On Saturday the tribunal, sitting in Manchester, declared that Dr Bonar's fitness to practise is impaired by reason of his misconduct.
Chair Ian Lewis said: "The tribunal found that you represent a potential future risk of harm to patients until you have reflected upon and understood your failures and demonstrated that you have remediated them.
"Accordingly, the tribunal determined that public confidence in the profession would be undermined and the tribunal would not be fulfilling its duty to declare and uphold proper standards of conduct and behaviour if these findings of serious misconduct did not result in a finding of impairment when your insight remained partial and you have not made sufficient efforts to remediate your failures."
Gary Summers, representing Dr Bonar, submitted the "very unusual set of circumstances" that his client found himself in was unlikely to be repeated.
He said Dr Bonar accepted that administering TPN in a home setting was "fraught with so many complexities" that he would not do it again.
Dr Bonar had the patient's best medical interests at heart throughout and his misconduct was not serious, he argued.
Safeguarding concerns were raised after two nurses complained about the woman's care and admitted her to hospital as an emergency on January 16.
She died two months later, although it was not part of the General Medical Council's (GMC) case that Dr Bonar's treatment shortened her life.
The GMC alleged that his treatment made her discomfort "worse rather than better" as she was treated ineffectively in "chaotic conditions".
A second doctor who treated Patient A at the apartment, Sussex-based GP Siegfried Trefzer, was also found to have administered TPN when it was dangerous to do so and without the assistance of a multi-disciplinary team or the supervision of an appropriate consultant.
The tribunal said his fitness to practise was not impaired as he had shown clear insight into his failings and had taken appropriate steps to remedy them.
The tribunal will reconvene at a later date to consider whether to impose a sanction on Dr Bonar's registration, which could include erasure.