(CNN) -- Major League Baseball is set to suspend some 20 players in the coming weeks due to a scandal involving performance-enhancing drugs, according to an ESPN report that said a key figure in the case is now ready to cooperate with investigators.
The network says it is potentially the worst drug-abuse case in the history of U.S. sports.
The league declined to comment to CNN but confirmed that an investigation is in the works.
The players union said Wednesday that players are being interviewed by baseball officials and are represented by attorneys.
"The commissioner's office has assured us that no decisions regarding discipline have been made or will be made until those interviews are completed," the union said in a written statement.
Baseball's highest-paid player, New York Yankee third baseman Alex "A-Rod" Rodriguez, as well as Ryan Braun of the Milwaukee Brewers, are among those facing suspension, ESPN said, citing unnamed sources.
Both have denied recently using performance-enhancing drugs, or PEDs. Rodriguez has admitted in the past to using banned substances when he played with the Texas Rangers in the early 2000s.
The league may seek to ban the players for 100 games by counting the doping itself as one infraction and lying about having taken the drugs as a second one, ESPN reported. Major league players can appeal any possible suspensions, as Braun did in 2012.
That year, a drug test showed high levels of testosterone in his body, but the outfielder successfully disputed the testing process, and the suspension was overturned in February.
Asked about the ESPN report Tuesday, Braun said he was sticking by his previous account. "The truth has not changed," he told reporters, declining to comment further.
CNN has not independently confirmed the ESPN report.
A Florida newspaper first leveled doping allegations at Rodriguez in January. The Miami New Times reported that the shortstop and third baseman had acquired the drugs from a now-closed Miami anti-aging clinic called "Biogenesis," run by Anthony Bosch.
ESPN said Bosch, who allegedly supplied baseball players with performance-enhancing substances, has agreed to cooperate in the MLB investigation. CBS Sports also confirmed Bosch will talk to investigators.
Records obtained by MLB name many players, but league investigators need Bosch to attest to their accuracy and confirm that players were doping, ESPN reported, citing unnamed sources.
The league filed a suit against Biogenesis in March for allegedly supplying PEDs to players and advising them on how to avoid detection during drug tests.
ESPN reported that MLB may drop the suit against Bosch, if he cooperates in its investigation.
On Tuesday, the managers for the Yankees and the Brewers said little.
"I know Major League Baseball is handling it, and that's all I know," Brewers manager Ron Roenicke told journalists at a post-game news conference in Milwaukee.
Yankees manager Joe Girardi started out dodging reporters who grilled him on ESPN's report after New York's game but softened when it came to his concerns about Rodriguez.
"I always worry about my players, always," he said. "One thing you never want to forget is -- they're human beings."
He did not say whether he had discussed the looming scandal with Rodriguez.
"When I talk to Alex, it's baseball-related. That's what it is," Girardi said.
He feared the game he has dedicated his life to will suffer because of the scandal.
"I worry about baseball being affected as a game, the whole thing, and what it's been through in the last 15 years."
Rodriguez was at the Yankees training facility in Florida on Tuesday, recovering from an injury. He could not be reached for comment. A 100-game suspension could cost him more that $15 million, ESPN reported.
New York outfielder Vernon Wells was discouraged by the scandal.
"We've done so much as a group to try to rid ourselves of conversations like this," he said.
In spite of advances in drug testing, new doping techniques designed to avoid detection keep coming, Wells said.
"There's always someone out there trying to beat the system from a medical standpoint."