Jeff Conaway is in critical condition at a Los Angeles hospital.
His manager, Phil Brock, said Thursday the 60-year-old actor was found unconscious on May 11, with initial reports citing a drug overdose - possibly from painkillers - as the cause of the hospitalization.
"Celebrity Rehab's" Dr. Drew Pinksy came to Conaway's defense Friday, tweeting, "Just visited Jeff Conaway. He is stable & looks like he will recover from his pneumonia.Not an OD like press is alleging & certainly not dead"
Dr. Pinsky also clarified the initial reports that Conaway was in a coma, tweeting that the actor is in an induced coma on a Propafol drip.
"Pneumonia with sepsis. No evidence of intentional OD."
In 2008 Conway appeared on VH1's "Celebrity Rehab" series, where he admitted his addiction to cocaine, alcohol and painkillers and talked about his sexual abuse as a child and his co-dependent relationship with his addict girlfriend Vikki.
During his second season on the show, Conaway left rehab before graduation and was seen taking painkillers after he arrived home.
Conaway began acting on Broadway at age 2, but it was his role as Danny's sidekick Kenickie in "Grease" that earned him fame.
He went on to star as out-of-work actor Bobby Wheeler in "Taxi."
After a number of television and film appearances, he landed another series playing Sgt. Zack Allan on "Babylon 5."