National League MVP Ryan Braun is facing a 50-game suspension after testing positive for a performance-enhancing drug, ESPN reported, citing two sources.
The league has not announced the finding because the Milwaukee Brewers star is disputing the result through arbitration, Saturday's report said.
"There are highly unusual circumstances surrounding this case which will support Ryan's complete innocence and demonstrate there was absolutely no intentional violation of the program," a spokesman for Braun said.
"While 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," the spokesman said. "But we are confident he will ultimately be exonerated."
Braun, 28, told USA Today, "It's BS." He reportedly was notified of the positive test in late October.
Sources said the result was triggered by elevated levels of testosterone in his system in an initial test and another, more comprehensive test found that those levels were not produced by his body.
Brewers chairman and principal owner Mark Attanasio released a statement Saturday night saying the team was "committed to supporting Ryan to get to the truth of what happened in this unfortunate situation."
"MLB has put a confidential testing program into place, which I personally support, that has a specific review process that must be followed before determining whether a player is in violation," Attanasio said, adding, "We are dealing with an incomplete set of facts and speculation. Before there is a rush to judgment, Ryan deserves the right to be heard."
Attanasio said the team was yet to be contacted by the commissioner's office or any official entity related to MLB testing programs.
Braun saw off the Dodgers' Matt Kemp to add the MVP trophy last month to his 2007 Rookie of the Year Award.
Kemp's agent Dave Stewart told the Los Angeles Times he hoped Braun is vindicated, but added, "If this thing turns out to be true and it turns out to be a fact that there were performance-enhancing substances in Ryan Braun, we're going to be disappointed."
Braun's award capped yet another elite season for the four-time All-Star, who finished first in the National League in slugging percentage with .597 and on-base plus slugging percentage (OPS) with .994.
His .332 batting average in 2011 was second in the National League only to former Mets shortstop Jose Reyes, who hit .337.
The slugger, who was drafted fifth overall by the Brewers in 2005, notched 33 home runs, 111 RBIs and 33 stolen bases last season, helping Milwaukee to 96 wins and the National League Central Division.
He was signed during the season to a five-year, $105 million extension.
Braun has displayed remarkable consistency since coming into the league in 2007, averaging 32 home runs, 106 RBIs and nearly 75 extra-base hits per season to go with a .312 career batting average.