"Taxi" and "Grease" star Jeff Conaway remains in a coma in a Los Angeles-area hospital, PEOPLE reported Friday.
Conaway, 60, apparently lay unconscious for 10 hours before being discovered last week at his home. Initial reports said he had pneumonia, although his representative told E! News that the actor may have overdosed.
"We are concerned it may have been an overdose but we have no way of knowing for sure," manager Phil Brock told PEOPLE. Brock said the actor turned his head over the weekend but his condition has not changed since then.
Conaway had struggled with health and addiction problems since he was 17, including breaking his hip in a 2010 fall when he was reportedly under the influence of methadone and OxyContin.
He appeared on multiple stints on "Celebrity Rehab with Dr. Drew." Also seen on the show was his girlfriend at the time, Vikki Lizzi. Radaronline.com reported Thursday that Conaway's family had filed a restraining order against Lizzi to keep her away from Conaway's hospital bedside.
"Celebrity Rehab" host, Dr. Drew Pinsky, told PEOPLE "I am deeply saddened to learn of Jeff's condition. My thoughts and prayers are with Jeff and his family.