Cops issued Miami Heat forward Haywood Highsmith a citation for careless driving on Tuesday ... after they say he caused an accident that resulted in a man suffering a partial amputation of his leg as well as other broken bones.

According to a crash report, obtained by TMZ Sports, the gruesome wreck happened at around 11:20 PM -- just minutes after Highsmith and the Heat beat the Orlando Magic at the Kesaya Center in Miami.

Cops state in the documents that Highsmith was going an estimated 45 MPH in a 40 MPH zone ... when he slammed into the back of a pedestrian who appeared to be pushing a broken-down car in the middle of a roadway.

The docs state Highsmith told officers that the disabled vehicle did not have its lights on ... and he couldn't stop his ride in time when he came across it in the street.

Cops wrote in the docs the pedestrian lost part of his right leg in the accident and sustained a compound fracture to his left leg as well. They also say the man suffered a possible broken left arm.

Police added the man was rushed to a local hospital in critical condition.

The crash report states drugs and alcohol were not involved ... though officers did write in the docs that Highsmith may have been distracted by unknown circumstances.

Highsmith logged three minutes of playing in the Heat's 121-95 win earlier in the night. He did not play Wednesday, though -- as the team announced he was sitting out of their game against San Antonio due to "personal reasons."