David Cornwell joined Jay Reisinger to represent Rodriguez in baseball's drug investigation.
The players' association filed a grievance on behalf of Braun and his positive drug test was thrown out by an arbitrator in February 2012 because the collector of the urine sample didn't take it directly to a Federal Express office on a Saturday evening, instead storing it at home until the following Monday.
Anthony Bosch, who was the head of Biogenesis of America anti-aging clinic, agreed this week to cooperate with Major League Baseball's investigation. He had previously denied any connection to the players or performance-enhancing drug distribution.
Rodriguez, Braun and more than 15 other players have been linked to the clinic, which was accused in January by the Miami News Times of providing the illegal drugs.
More from the AP:
Bosch was to meet Friday in Miami with MLB officials, another person familiar with the investigation said, also on condition of anonymity because no statements were authorized.