Alex Rodriguez with the New York Yankees, Ryan Braun with the Milwaukee Brewers, Nelson Cruz with the Texas Rangers and Melky Cabrera with the Toronto Blue Jays are among the players whose names have been tied to the now-closed Biogenesis of America.
The probe into players taking banned substances has been ongoing, but now it looks like investigators have their smoking gun.
According to ESPN, clinic owner Anthony Bosch told investigators he even injected Rodriguez himself.
In the past, many players under scrutiny have denied any kind of illegal use. Tuesday night, Braun didn't say much more.
"I've dealt with this off and on for the last year and a half, I guess and aside from that I don't really have anything further to say," said Braun.
ESPN reports that Bosch is now cooperating with investigators after being sued by the league, which is accusing him of scheming to provide banned performance enhancing drugs to players in violation of their contracts.
According to ESPN, Rodriguez and Braun may face a 100-game suspension instead of the standard 50, because the players allegedly broke two rules - doping then lying about it.
The MLB Commissioner's Office is able to suspend players even without the player actually testing positive. All it needs is proof they used a banned performance enhancing drug, possessed one or did business with someone like Bosch and then lied about it.
The Associated Press contributed to this report.