Golden Boy Promotions CEO Richard Schaefer has confirmed the findings but refused to disclose the nature of the substance.
Ben Thompson of FightHype.com is reporting that Morales' A sample tested positive and the results of the B sample should be known tomorrow.
Schaefer told SI.com that the U.S. Anti Doping Agency (USADA) informed Golden Boy two days ago of the irregularities. And yesterday, USADA told both camps and the New York State Athletic Commission of the positive test.
"USADA has now started the process," Schaefer told SI.com. "The process will play out. There is not going to be a rush to judgement. Morales is a legendary fighter. And really, nobody deserves a rush to judgement. You are innocent until proven guilty."
As of this writing, the bout is still on.
Erik Morales is scheduled to face RING/WBC/WBA Jr Welterweight Champion Danny Garcia in a rematch Saturday in the main event of a four world title fight card at the new the $1 billion Barclays Center in Brooklyn.
Will Performance-enhancing drugs derail another big fight?
If the fight happens and Morales did, in fact, fail his drug testing, its likely Garcia's WBA and WBC titles will not be contested.
Last March, in the first meeting between the two, Morales failed to make weight, so some are speculating if the Mexican legend used a banned diuretic.
Lastly, as Schaefer stated, the results are preliminary and there shouldn't be a rush to judgment until more is known.
UPDATE: Morales has tested positive for an anabolic steroid, according to a person with knowledge of the test results who spoke to USA TODAY on the condition of anonymity.