ESPN cited two sources Saturday in first reporting the news, saying the 28-year-old Milwaukee Brewers star tested positive for elevated levels of testosterone.
A spokesman for Braun said in a statement that "there are highly unusual circumstances surrounding this case which will support Ryan's complete innocence."
Ryan Braun
"There was absolutely no intentional violation of the program," Matthew Hiltzik said in a statement sent by the four-time All-Star left fielder's representatives.
"Ryan has impeccable character and no previous history, unfortunately, because of the process we have to maintain confidentiality and are not able to discuss it any further."
"we are confident that he will ultimately be exonerated."
The case is still being appealed to an arbitrator under MLB's drug program.
Major League Baseball does not announce positive tests and penalties in drug cases involving initial positives until all arbitration issues are concluded.
The people spoke on condition of anonymity because the appeal is still ongoing and said Braun has known about the positive test since late October.
One of the people involved said that the appeals process regarding the outfielder's case is not likely to be concluded until January at the earliest.
That person said after being informed of the positive test, Braun asked to have another urine test taken, and that test was within normal range.
If suspended, Ryan Braun wouldn't be eligible to play for the NL Central champions until May 31 at Dodger Stadium, barring any postponements.
The 50-game suspension means he would miss the first 57 days of the major league season, losing about $1.87 million of his $6 million salary.
He hit .312 with 33 homers and 111 RBIs in 2011 and led Milwaukee to the NLCS, where the Brewers lost to the eventual World Series champion Cardinals.
