Owner Ann Budge says Hearts "could be facing up to six months of totally abnormal operations" that will not be survived without wage reductions.
Hearts asked players and other staff to accept reduced terms while football is on hiatus because of coronavirus, with captain Naismith taking a 50% cut.
"I see absolutely no reason for sitting back and waiting either on a miracle or for the government to bail out every company in the country in a timely enough manner," Budge told the club's website.
"Neither of these options is likely to happen and, therefore, I make no apology for putting immediate plans in place to mitigate the problems heading our way.
"For the sake of our supporters I need to address the enormous amount of ill-informed and self-opinionated commentary coming from some sections of the media at the moment."
Scottish football was suspended on 13 March and Budge insists Hearts, who are bottom of the Premiership, are "no worse (nor better) than almost every other senior football club in Scotland".
However, after approaching their bank, she said the club had been unsuccessful in securing more funds.
"Having approached our bank we have been formally advised that their policy towards football clubs hasn't changed and they remain unable to lend to us," said Budge. "I would stress that we are not alone in this. This is not a Hearts problem; it is a football problem."
She added: "Payroll, as with all clubs of our size, is by far our biggest monthly cost. There is little doubt that we will have to implement a salary reduction programme across the club. We simply will not survive a six-month close down, unless we implement this.
"I have been roundly criticised for even suggesting such a thing. However, our staff have been amazing. A number of staff and managers offered to take no salary or a larger wage reduction to enable us to better support those who needed it more.
"I asked all employees to stand together to ensure we can survive the next few months. Most of the staff agreed immediately.
"Given the added complexities around players' contracts and the wide range of personal circumstances, a number of players are still reviewing their situations. However, I believe we will reach a good outcome as I know they want to do what they can to support the club."
Budge added the club will be selling season tickets for the next campaign "as soon as we can".