Sources told US publication People that he is "deeply concerned for Demi".
"He still cares about her and wants the best for her. But their marriage is ending and they are both moving on with their lives," said one friend.
The 33-year-old was the first to comfort Demi when her good friend, substance abuse counsellor Pattsy Rugg, died in December.
The 70-year-old had apparently become like a mother figure to the devastated actress.
Ashton was in Brazil to film an ad campaign (pictured above) when he heard about his former partner's health scare.
He also attended a Florence and the Machine concert and went to see his pregnant model friend Alessandra Ambrosio strut her stuff at Sao Paolo Fashion Week (below).