MLB opened an investigation Monday into allegations that former Los Angeles Angels infielder David Fletcher gambled with an illegal bookie, an MLB source told ESPN, but investigators face a significant hurdle at the start — where they’re going to get evidence.

ESPN reported Friday that Fletcher, who is currently playing for the Atlanta Braves‘ Triple-A affiliate, bet on sports — but not baseball — with Mathew Bowyer, the Southern California bookmaker who took wagers from Shohei Ohtani‘s longtime interpreter, Ippei Mizuhara.

Fletcher’s close friend Colby Schultz, a former minor leaguer, also bet with Bowyer and wagered on baseball, including on Angels games that Fletcher played in while he was on the team, according to sources.

MLB investigators will request an interview with Fletcher at some point, but he has the right to refuse cooperation if he can claim he could be the subject of a criminal investigation.

Fletcher did not respond to multiple requests for comment Friday.