Pierre-Gabriel, 22, signed on a season-long loan from Bundesliga club Mainz on July 7 but was involved in a serious incident on Monday evening.
On Tuesday, as Brest statement on social media read: "Last night, in the Brest neighbourhood, Ronael Pierre-Gabriel was the victim of an assault and suffered injuries before his car was burned down and completely destroyed.
"Brest strongly condemn this event and give its full support to Ronael.
"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 also said it would be the last time they would comment on the issue and have left the situation to the authorities.
Pierre-Gabriel made eight appearances for Mainz this season but failed to feature for the first team after the Bundesliga restart following the suspension caused by the coronavirus pandemic.
Brest were in 14th position in the league table before the Professional Football League (LFP) ended 2019-20 Ligue 1 and Ligue 2 seasons in April.