Major League Baseball's players' association is conducting an investigation into the role some agents might have played in the Biogenesis doping scandal that rocked the sport last year, several sources told ESPN.

The MLB Players Association, which certifies player agents, retained veteran Washington attorney Robert Muse to run the investigation several months ago, the sources said, and he and his staff are expected to issue a report within the next few weeks.

According to sources, who spoke on the condition of anonymity, the two primary subjects of the investigation have been the ACES agency out of Brooklyn, run by longtime agents Seth and Sam Levinson, and CAA in Los Angeles, where agent Nez Balelo represents Ryan Braun. Braun, who plays for the Milwaukee Brewers, accepted a 65-game suspension for PED use last year.

If the agents are found to have been complicit or to have violated their duties, they could face decertification, although the MLPBA's agent regulations also allow for lesser penalties.

MLBPA general counsel David Prouty declined to confirm the existence of the investigation, saying, "We don't comment on internal investigations or whether we're conducting them."

A spokesman for MLB described the investigation as "an internal union matter" and referred questions to the MLBPA.