Jeff Conaway, of ‘Grease’ and ‘Celebrity Rehab,’ in coma

60-year-old Jeff Conaway, who appeared on Dr. Drew’s reality-treatment show Celebrity Rehab, is currently in critical condition in a coma, according to The Hollywood Reporter.

Conaway is probably best known as “Kenickie” in the movie musical Grease, and also appeared on Taxi. His career faltered during the 80’s and 90’s, as the actor struggled with substance abuse issues. On Celebrity Rehab, the actor battled with addictions to cocaine, alcohol and painkillers. In 2010, he broke several bones in a fall down a staircase and suffered a brain hemorrhage.

His manager declined to disclose specific details, but confirmed that the coma stemmed from an overdose, and said the actor’s prognosis is “uncertain”:

Phil Brock said the 60-year-old actor was found unconscious May 11. He is hospitalized in critical condition.

Brock added that Conaway is in a coma in a California hospital and his recovery is uncertain. The name of the hospital was not disclosed.

Brock says Conaway initially turned his head, but has not been responsive for days.