10:35 AM PT -- TMZ Sports has obtained the mug shot from Herrera's arrest.

We've also obtained court docs from the incident ... which say Herrera's girlfriend was found with "hand print markings to her neck area and small scratches to her arms."

Odubel is due in court to face the charge in June on the same day the Phils are scheduled to play the Nationals in D.C.

Philadelphia Phillies outfielder Odubel Herrera was arrested Monday night after cops say he roughed up his 20-year-old girlfriend during an altercation in an Atlantic City casino.

According to the Atlantic City Police Department, Herrera and his GF got into a dispute at the Golden Nugget Hotel and Casino during the Phillies' off day Monday.

Cops were called to the scene ... and when they saw the woman, they said she had visible injuries on her arm and neck.

Cops say they found 27-year-old Herrera in his hotel room after the incident ... and arrested him on the charge of simple assault.

Herrera -- who's batting just .222 with 1 home run for the Phils this season -- was released from custody shortly after and will be required to return for a court date in the future.

For their part ... Major League Baseball says it's placed Herrera on administrative leave in wake of the arrest.

"This morning we were made aware of an alleged incident involving Odúbel Herrera," the Phillies said in a statement ... "Upon receiving this information, we immediately reported the incident to Major League Baseball, which has informed us that Herrera has been placed on Administrative Leave."

"The Phillies take any domestic violence accusation seriously, and strongly support the Joint Domestic Violence Policy agreed upon by MLB and the MLBPA."