The South African-based businessman, who has concerns over the Ibrox club's plan to borrow £1.5 million from two shareholders, has repeated an earlier offer to fund the League One club's rebuilding programme.
Mr King believes the board has not been transparent with supporters over the club's financial state and has called on fans to "draw a line in the sand".
Rangers have agreed to the loan facility provided by Sandy Easdale, the Rangers FC chairman, and Laxey Partners, the largest single shareholders in Rangers International Football Club.
It would mean Laxey receives a 15% premium on its £1m loan, secured against the club's Edmiston House office complex and the Albion car park, effectively a profit of £150,000.
Mr King, who has offered to provide significant investment by way of a fresh share issue, said the board's previous "categoric assurances there was sufficient funding until the end of the season were untrue and that emergency financing has been put in place on terms that are not commercial".
He has called upon fans to "protect themselves but still assist the team and management" by either putting their season ticket renewal money into a trust fund that releases the money to the club on a "pay-as-they-play basis" or releases it in full "but against the security of the club property until such times as all games are played".
"The purchase of a season ticket is essentially an individual loan from the fan to the company until such time as all games are played," Mr King said. "Unless the board departs from its present stance of opacity, the fans will be asked to lend money to the company with no security and with no comfort that [it] is not going into a financial black hole.
"The board was happy to give security to Laxey Partners as well as a massive return on this short-term loan. It seems wrong that these new loans will be repaid from interest free and unsecured loans provided by long suffering fans."
The Rangers supporters organisations intend to publish their full response to King's call to arms today, but Drew Robertson of the Rangers Supporters Association said: "It's the Albion car park and Edmiston House, how long before it's Auchenhowie and Ibrox?"
In a statement, the Rangers board said: "The board notes Mr King's comments with concern as they are potentially de-stabilising and damaging to Rangers Football Club."