Domingo German, one of the Yankees’ best starting pitchers this season, was placed on administrative leave on Thursday under M.L.B.’s domestic violence policy, the league office announced. The move, which temporarily bars German from playing, is a precursor to a larger investigation, which could lead to a suspension.

M.L.B. did not detail the circumstances that had led to the investigation, but two people with knowledge of the situation said that the league had become aware of an incident involving German and a woman earlier this week. During an initial inquiry, league officials quickly found what they felt was sufficient evidence to place German on leave Thursday afternoon, though a police report had not been filed, according to the people, who requested anonymity to discuss details of an active investigation.

The incident that led to the inquiry occurred sometime between Monday night and before the Yankees’ game on Tuesday night, according to one of the people. M.L.B. launched its initial inquiry when it learned about the incident from someone who had been told about it by the woman involved, the person said.

The players’ union, which has the right to challenge a player’s administrative leave, is not doing so now, according to a person with knowledge of the union’s thinking who was not authorized to discuss it publicly.