Atlanta Braves general manager John Coppolella has resigned “as a result of a breach of MLB rules regarding the international player market,” the team announced in a statement Monday.

“Major League Baseball is investigating the matter with our full cooperation and support,” Braves President of Baseball Operations John Hart said in the statement. “We will not be issuing any further comment until the investigation is complete.”

Hart will perform the Braves’ GM duties while the club searches for Coppolella’s replacement.

The details of MLB’s investigation into the case are as yet unclear, but the league’s latest collective bargaining agreement includes a hard cap on the amount of money that teams may spend on international prospects. In July 2016, the Red Sox were found guilty of inflating their signing bonuses for prospects and was prohibited from signing international amateur players for one year. Yahoo’s Jeff Passan reports that MLB’s investigation of Coppolella also includes his “treatment of Braves employees.”

The 38-year-old Coppolella began his career as an intern in the Yankees’ front office, joined the Braves as the club’s director of baseball operations in 2006 and was promoted from assistant general manager to general manager after the 2015 season. He and Hart helped rebuild Atlanta’s minor league system after general manager Frank Wren was fired after the 2014 season. The Braves, who last qualified for the playoffs in 2013, committed to a rebuilding project, trading away high-priced veterans for prospects. The Braves entered the 2017 season with the league’s top-ranked minor league system, but lost at least 90 games for a third consecutive year.

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