Speculation about the state of the couple's marriage was sparked by reports that Kutcher slept with 23-year-old Sara Leal on their sixth wedding anniversary last month.
Moore went on to post a series of cryptic messages seemingly hinting at their relationship problems, but both stars have since denied rumours of a divorce and continued to appear together in public.
However, The Mail On Sunday claims to have been told by an "entertainment industry insider" that Moore is making preparations for the split.
"Miss Moore has been totally humiliated. On Friday, therefore, she consulted a lawyer about getting a divorce," the source said.
"This is a huge and very tough decision for Miss Moore to take. But her trust has been shattered. She desperately wanted to save their marriage... But it hasn't worked. She is done with him."
The source added that both Moore and Kutcher are estimated to be worth approximately £97m.
Moore's publicist and film industry lawyer have failed to comment on the latest rumours.