Whyte withdrew from a press conference to promote the November 30 bout after learning he had tested positive for methylhexaneamine or DMAA, and could now face a ban by the British Boxing Board of Control.
The 24-year-old Whyte insisted the trace must have come from an energy drink which was banned from public sale only a matter of weeks before his positive test.
Whyte said: "I have nothing to hide. It is a genuine mistake and I urge all boxers to double-check all ingredients in all pre-workout drinks they take. I would hate to see another boxer make the same mistake I have."
Whyte insists he will co-operate fully with the UK Anti-Doping Agency as well as the Board, but his positive test means it is highly likely his big bout against McDermott is off.
Whyte's manager Joe Long said: "This is a sickening setback for Dillian and a big lesson to be learnt. We will be meeting with the UK Anti-Doping Agency later this week and hope to come to a conclusion ASAP."