By Mark Lamport-Stokes

LOS ANGELES (Reuters) - Major League Baseball (MLB) has launched an investigation after Atlanta Braves pitching coach Roger McDowell was accused of "highly inappropriate conduct toward fans" by a man on Wednesday.

According to Justin Quinn, McDowell made homophobic comments and crude sexual gestures to three male fans sitting in the bleachers during pre-game batting practice at AT&T Park in San Francisco on Saturday.

Quinn, who was also in the stands with his wife and their nine-year-old twin daughters, complained about the behavior before McDowell allegedly threatened to knock out his teeth with a baseball bat.

"Although I do not yet have all the facts regarding this incident, the allegations are very troubling to me," MLB Commissioner Bud Selig said in a statement.

"The Atlanta Braves have assured my office that they will immediately investigate the allegations, and report the results of the investigation to me. After I have all the facts, I will make a determination of how to proceed."

In a statement issued by the Braves on Wednesday, McDowell said: "I am deeply sorry that I responded to the heckling fans in San Francisco on Saturday. "I apologize to everyone for my actions."

Quinn, 33, described what took place at AT&T Park during a news conference with his attorney Gloria Allred in Los Angeles on Wednesday.

Appalled by McDowell's behavior toward the three male fans, Quinn called out: 'Hey, there are kids out here'. He alleged that the pitching coach replied: "Kids don't **** belong at the baseball park.'

According to Quinn, McDowell then picked up a baseball bat, walked up to him and asked: 'How much are your teeth worth?'"

In a statement, Quinn said: "When I go to a baseball game and take my family, I expect a higher standard of conduct from the team and its coaches.

"Children should not be told they do not belong at a ballpark. Major League Baseball should not tolerate this kind of disgusting and offensive conduct and that is why I am speaking out today."

(Editing by Julian Linden)