According to the letter, obtained by the Telegraph, Mr Ashley offered Debenhams a £40m interest-free loan, which was rejected.
In his message, the Sports Direct owner said: “November was the worst November for retailers in living memory.”
He went on to list a number of Debenhams’ perceived shortcomings: “The market is saying that [Debenhams has] got no credit insurance, advisers and the banks are telling key suppliers that they shouldn’t trade with you at a level above which they can afford to lose, the suppliers are managing themselves out of stores and, at the same time, you’re discounting product in an effort presumably to try and realise some cash.
“Additionally it is speculated that the company currently has a zero chance of survival.”
Earlier this year, Debenhams announced plans to close up to 50 shops, putting 4,000 jobs at risk.
The cuts are being made in an attempt to slash costs, after the company reported its biggest ever loss of £492m in the year to 1 September.
Sports Direct currently holds 29.7 per cent of Debenhams, just shy of the 30 per cent threshold at which an offer for the remainder of the company must be made, according to the UK takeover code.
Mr Ashley said in his letter that he was concerned that the Debenhams board “doesn’t really seem to appreciate” the position that the company is in “and their responsibility to shareholders”.
He added: “Sports Direct is Debenhams’ largest shareholder. What we are offering is a very public statement of support at a critical time for the Debenhams business.”
The letter concluded with a request that Mr Bucher reconsider the offer of a loan, and respond by “lunch time Friday”.
A spokesperson for Debenhams said: “We welcome Sports Direct’s proposal as a clear demonstration of their willingness to support the company.
“However, as the offer came with conditions that could affect the interests of other stakeholders, while the board does not think it could accept the proposal, as presented, it has invited Sports Direct to engage as part of our broader refinancing process.”
Shares in Debenhams were down 4.89 per cent to 5.45 at close of trading on Thursday, while Sports Direct’s stock tumbled by 14.8 per cent to 235.40.
Earlier in the day, Sports Direct issued a trading update for the first half and revealed that House of Fraser had lost £31.5m in the first 11 weeks after the discount retailer bought it out of administration.
Sports Direct also recently purchased Evans Cycles from its administrators.
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