Major League Baseball has opened a formal investigation into the matter surrounding Los Angeles Dodgers superstar Shohei Ohtani and his former interpreter, Ippei Mizuhara, the league announced Friday.

MLB is expected to request interviews with all parties, including Ohtani and Mizuhara, a source told ESPN, although officials will have no way to compel Mizuhara's cooperation since he no longer works for baseball.

Ohtani also has a right to refuse cooperation as a member of the MLB Players Association. Ohtani also could invoke his right, under an interpretation of arbitration precedent, to refuse cooperation because of a criminal investigation that's already underway. Traditionally, MLB has argued a player can invoke such an exception if he is a target of the investigation, which Ohtani is not believed to be.

Major League Baseball said in a statement that it began gathering information about the allegations involving Ohtani and Mizuhara after reports came out this week. Its Department of Investigations began formally investigating the matter Friday, the league said.

The announcement came two days after Mizuhara was fired by the Dodgers as reporters pressed for questions about at least $4.5 million in wire transfers sent from Ohtani's bank account to a bookmaking operation that is under federal investigation.

In a span of two days, Ohtani's handlers moved from saying the slugger had paid Mizuhara's gambling debts to his attorneys announcing Ohtani had been the victim of a "massive theft."

It remains unclear if any authorities are investigating the alleged theft. Ohtani's representatives said Thursday they had officially submitted the allegation to law enforcement but did not say to which authorities. Multiple sources told ESPN that neither the California Bureau of Investigation nor the FBI was working the case.

Spokespersons with the Los Angeles Police Department and district attorney's offices in Los Angeles and Orange counties all said they were not investigating, and they indicated it was most likely a federal matter. The U.S. Attorney's Office for the Central District of California declined to comment.

Ohtani is expected to remain on the Dodgers' active roster while the league's investigation unfolds.

MLB's administrative leave, whereby players are paid their salaries but are ruled ineligible to play while investigations are ongoing, applies only to issues pertaining to the joint domestic violence, sexual assault and child abuse policy. Because Ohtani has not been accused of dealing directly with the bookmaker and there is no evidence that any of the bets were made on baseball, the league doesn't see a need to take him off the field at this moment.

ESPN's Alden Gonzalez contributed to this report.