[undefined]Justin Bieber is reportedly under police investigation [Getty]
The Sorry singer was reportedly caught up in an altercation outside a pre-Grammys event, with ITVstating that Justin, 22, was involved in separate altercations with two bartenders in Hollywood.
According to ITV, the Sheriff’s Department stated: "The witness said he broke up the fights and asked Mr Bieber to leave. 
"Mr Bieber refused to leave and remained at the restaurant.
"The witness stated, a few minutes later, he saw Mr Bieber arguing with a patron, when Mr Bieber suddenly headbutted the patron."
[undefined]Justin Bieber allegedly 'headbutted' someone [Wenn]
According to the Sheriff's Department, the witness said Justin left the location after pals pulled him away from the alleged victim. 
The bartenders allegedly involved in the incident had left the scene, according to the witness.
Officers reportedly interviewed the alleged victim, but he refused medical attention and did not want to file a police report.
[undefined]Justin Bieber 'left the scene' after the incident[WireImage]
There were "no visible marks on the man" and detectives are continuing to gather evidence, the Sheriff's Department added.
According to TMZ, the alleged victim doesn't want to press charges against Justin.