Sports Direct, Debenhams' largest shareholder with a near 30 percent stake, has been trying push for control of the group, but an attempt to appoint Ashley to the board and replace nearly all of the existing directors failed because Sport Direct at the time owned its stake through a third-party nominee.
Debenhams, which has issued a string of profit warnings and has lost 90 percent of its market value in the last year, is pursuing its own refinancing plan, but it warned on Friday that existing shareholders could be wiped out.
"In Sports Direct's opinion, Debenhams restructuring and refinancing process is likely to result in an adverse outcome for Debenhams existing shareholders," the sports retailer said on Monday.
"Accordingly, Sports Direct confirms that, alongside other options, it is considering a possible offer for the entire issued and to be issued share capital of Debenhams not already held by Sports Direct."
Billionaire Ashley, who also owns Newcastle United football club, made his fortune from building his sportswear chain.
More recently he has invested in other retailers hit by the rapid shift online and subdued consumer spending in Britain, including Debenhams' department store rival House of Fraser.
Under British takeover rules Sports Direct has until April 22 April to either make a firm offer or walk away.
Sports Direct said any offer would likely be in cash.
(Reporting by Sangameswaran S in Bengaluru and Paul Sandle in London; Editing by Anil D'Silva and Jane Merriman)