The world renowned swimmer, who won eight gold medals at the 2008 Olympic Games in Beijing, was found to have an arm span measuring 6 feet 7 inches - some 12 inches longer than the average swimmer.
In a statement made on his website today, Phelps issued an apology to the International Olympic Committee and his millions of fans worldwide.
"I wholeheartedly and unreservedly apologize for what I know is an unacceptable physique in the world of swimming," read his statement. "It is one thing to try and gain an advantage over your opponents, but to be born with, and later develop, such unusually long arms is truly against the ethics of this great institution."
"Just... what have I done?"
The IOC is set to announce its ruling Tuesday afternoon, with the possibility that Phelps could receive a ban of up to two years as well as a period of rehabilitation aimed at reducing his considerable physical stature.
Meanwhile, the announcement comes just two weeks after Special Olympics 100 Meters sprinter Adekunle Adesoji was banned for 10 months after testing positive for performance enhancing legs.
Image credit: Flickr, jdlasica