Mizuhara is a familiar face to baseball fans and has served as Ohtani's interpreter since the Japanese pitcher and designated hitter arrived in the U.S. in 2017.
When Ohtani left the Los Angeles Angels to sign a record 10-year contract with the Dodgers in December, the club also hired Mizuhara. He was in the Dodgers' dugout during Wednesday's season opener against the San Diego Padres in Seoul, South Korea.
The Dodgers released a statement after the allegations surfaced saying they were "aware of media reports" and were "gathering information."
"The team can confirm that interpreter Ippei Mizuhara has been terminated," the statement said. "The team has no further comment at this time."
On Tuesday, Mizuhara told ESPN his bets were on international soccer, the NBA, the NFL and college football. MLB rules prohibit players and team employees from wagering — even legally — on baseball and also ban betting on other sports with illegal or offshore bookmakers.
"I never bet on baseball," Mizuhara told ESPN. "That’s 100%. I knew that rule. ... We have a meeting about that in spring training."
Ohtani's attorneys said Mizuhara placed wagers with Orange County, California, resident Mathew Bowyer, who is under federal investigation. Bowyer's attorney, Diane Bass, said her client "never met, spoke with, or texted or had any contact in any way" with Ohtani, according to the Los Angeles Times.
Ohtani is expected to remain on the Dodgers' active roster during the probe.
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Fox News' Ryan Morik and The Associated Press contributed to this report.