The actor sparked concern for his wellbeing last month when he disappeared for more than a week, prompting a police search for the star in Los Angeles.
Stahl, who has ongoing drug issues, subsequently reached out to his loved ones to assure them he was well, and his wife Rose Murphy Stahl revealed he had checked into a rehabilitation centre.
However, the actor has now allegedly left the clinic, with a source telling E! News, "He left a week ago. He walked out against doctors' advice. He just didn't want to be there anymore. It is very sad. He's still struggling and has yet to hit rock bottom. Everyone is extremely worried about him.