NEW YORK -- National League MVP Ryan Braun's 50-game suspension was overturned Thursday by baseball arbitrator Shyam Das, and sources told ESPN that Major League Baseball is weighing the possibility of suing in federal court to reverse the decision.

Braun's case marks the first time a baseball player has successfully challenged a drug-related penalty in a grievance.

The decision was announced Thursday by the Major League Baseball Players Association, one day before the 28-year-old outfielder reported to spring training with the Milwaukee Brewers in Maryvale, Ariz.

Braun tested positive in October for elevated testosterone, and ESPN's "Outside The Lines" revealed the positive test in December. Braun is expected to hold a news conference at 1 p.m. ET Friday, the team said.

"I am very pleased and relieved by today's decision," Braun said in a statement. "It is the first step in restoring my good name and reputation. We were able to get through this because I am innocent and the truth is on our side.

"We provided complete cooperation throughout, despite the highly unusual circumstances. I have been an open book, willing to share details from every aspect of my life as part of this investigation, because I have nothing to hide. I have passed over 25 drug tests in my career, including at least three in the past year."

In his appeal, Braun didn't argue evidence of tampering and didn't dispute the science, but argued protocol had not been followed. Multiple sources confirmed to ESPN investigative reporters Mark Fainaru-Wada and T.J. Quinn that Braun questioned the chain of custody and collection procedure.

MLB officials argued that there was no question about the chain of custody or the integrity of the sample, and that Braun's representatives did not argue that the test itself was faulty.

But multiple sources said the sample was not shipped for testing as soon as possible, as required by the drug testing policy, and instead was kept in a cool place in the sample collector's home. Sources told ESPN legal analyst Lester Munson that the collector left Braun's sample on a desk in a Tupperware container and left it there for two days.

Sources also told Munson that there was doubt over whose urine was actually being tested. Braun offered to take a DNA test to confirm whose urine was in the sample, but Major League Baseball declined. However, an MLB source told ESPN's Mike Golic that Braun's side backed off of the offer to take a DNA test.

Braun was "ecstatic" about the arbitrator's decision, his Brewers teammate and friend Corey Hart said Thursday night, according to the Milwaukee Journal Sentinel. Hart told the newspaper that Braun called him shortly after the decision was announced.

"It's an emotional thing, anytime your reputation is at stake. The whole situation is just kind of a screwed-up situation. It wasn't your normal case," Hart said, according to the Journal Sentinel.

"I'm sure he could have come out and said a few things that could have helped him out a little bit. He did what he had to do, and I'm sure he's going to have a lot to say (Friday) and the next day to help clear this up. But ultimately he's going to be playing, and we're going to be a much better ballclub because of it."

Early Friday, Braun's former Brewers teammate Prince Fielder, now with the Detroit Tigers, told ESPN.com's Jayson Stark the development was "great news," though he acknowledged he did not follow the case closely.