Pierre-Gabriel, who signed a short-term deal with Brest on July 7, was injured Monday night in the town located in France's Brittany region, his new club said in a statement Tuesday.
"Last night, in the Brest neighborhood, Ronael Pierre-Gabriel was the victim of an assault and suffered injuries before his car was burned down and completely destroyed," Brest's statement read, per ESPN UK.
"Brest strongly condemn this event and give (their) full support to Ronael," the statement continued.
"In a place where these events are few and far between, it's regrettable to see these types of incidents happen to a boy who only arrived two weeks ago in Finistere and had no issues with anyone."
The club did not offer any additional details, adding that the matter is now in the hands of authorities.
Pierre-Gabriel, 22, featured eight times for Bundesliga side Mainz this season, but he didn't appear in any of the club's nine matches after the restart in mid-May.