Sources say that neither star has filed for divorce or tried to legally separate, but that "they're taking a break."
The power couple has not been photographed together since April 22. Zeta-Jones has been seen on the red carpet alone and both have been seen on vacation with their children, Dylan, 13, and Carys 10, but never together.
Though they have been married since 2000, Douglas' three-year cancer battle and Zeta-Jones' recent struggle with bipolar II disorder have reportedly been tough on their relationship. A friend tells People, "The stress has taken a toll on their marriage."
A few other U.K. tabloids have been reporting recent rocky patches for Zeta-Jones and Douglas, but nothing was as concrete as People's report.
HuffPost has reached out to Zeta-Jones and Douglas' reps but did not receive immediate comment.
For more on the split, see the full story in People magazine on newsstands Friday (Aug. 30).
UPDATE: Catherine Zeta-Jones' rep tells HuffPost Celebrity, "Catherine and Michael are taking some time apart to evaluate and work on their marriage. There will be no further comment."