Following the pair's feud on Twitter yesterday, Michael told E! News that he is using text messages and social networking sites to urge Lindsay to get professional help.
"I'm not going to sit back and watch my daughter die or fall victim to something that so many other kids did," he said.
"She's going to a rehab, there's no doubt. My daughter's going to a rehab and she's going to get better. Doesn't matter how many times you go, but it has to be done the right way. I want her to be willing to do it on her own, and it seems that she's living in denial. She thinks it's okay and everyone says she's fine. But is she fine? Is Lindsay Lohan fine? Tell me I'm wrong and then I'll stop."
Michael claimed that his daughter has told him that she is taking prescription drugs for depression and attention-deficit disorder and added that his ex-wife Dina uses their children "as pawns".
He continued: "I didn't want to say anything about her assistants and the people around her but I think they're turning a blind eye and that's enabling. First I thought it was Lindsay but now it happens to be the people around her that I'm trying to get out of her life."
Michael concluded: "She went from such a vibrant, wonderful, beautiful, beautiful, beautiful, caring, loving and inspirational woman to the exact opposite."
> Lindsay Lohan dad 'makes rehab ultimatum'