Los Angeles - Michael Lohan collapsed during an Alcoholic's Anonymous meeting on Tuesday.
The showbiz patriarch - who had to undergo heart surgery earlier this month - became light headed during the meeting and when going outside for air, found himself unable to walk.
An ambulance was called and Michael was taken to hospital.
A source told RadarOnline.com: "Michael started to feel light headed during his meeting so he walked outside, and that's when he collapsed.
"He was taken in an ambulance to Palm Beach Gardens Hospital where doctors found another blood clot in his lung."
Michael - who is the father of troubled actress Lindsay Lohan - was given medication to break down the clot and had an MRI scan to check it hadn't spread to his brain.
The source added: "Michael's still waiting on the test results and we're not sure when he'll be released from hospital."
He had to be rushed back to hospital just hours after his heart surgery in early December when he was found to have a bacterial infection.
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