The Chicago actress, who cut short a trip to the Ryder Cup in order to return to her 66-year-old partner's side, is said to be desperately trying to avoid abandoning Douglas again while he undergoes treatment for throat cancer.
A family friend told the News of the World: "We are now gravely concerned about Michael's condition. All Catherine cares about is being with him and the kids.
"She had to go to Wales because of a contract. She didn't want to leave her husband, and in the end the separation was too much for her to cope with. She's a complete mess as you'd expect."
The source added that Zeta-Jones has managed to remain resilient throughout the ordeal thanks to the love of her family and the bravery that her husband continues to display.
"They are with her full-time at the moment to give her as much support as possible. Pat (Zeta-Jones's mother Patricia Fair) has been saying, 'I've never seen her like this. She's so upset.'
"Catherine is now doing everything possible to get out of having to travel again. She has one more event, in China. We're hoping the organisers will show some sympathy and let her stay with Michael. Catherine is taking a lot of strength from how brave he's being."
