Renowned political and social critic Somsak Jeamteerasakul has collapsed and been hospitalised after a stroke.
Pavin Chachavalpongoun posted messages on his Facebook account on Sunday saying Mr Somsak was in a hospital in Paris after a stroke left him unable to move the right side of his body.
Doctors gave him medication to reduce his blood pressure and will conduct an MRI, said Mr Pavin, citing information from friends in the French capital.
Mr Somsak will need rehabilitation and it was too early to tell whether he would regain full use of his body, said the lecturer on Southeast Asian studies at Kyoto University.
Mr Somsak was an active social critic, posting comments about Thai politics and society on his Facebook page. His last post on the social media site was on Thursday.
The former Thammasat University lecturer is a staunch critic of the regime and the lese majeste law. He left the country after the coup in 2014 due to concerns over his safety.