The company, which has a market cap of less than £5mln, had been exploring ways to refinance its £220mln bond debts when they mature next June.
Credit agencies had previously said that this would be nigh-on impossible and Johnston has now conceded that putting itself up for sale is the only option.
The firm has seen the value of its titles, which include the ‘i’, The Scotsman and the Yorkshire Post, tumble in recent years following a decline in traditional and digital advertising revenues.
In its latest results, Johnston Press reported a 10% fall in revenues during the first half of 2018.
It swung back to a profit of £6.2mln for the six-month period, but this was almost entirely due to a one-off accounting gain of £8.8mln.
Custos Group, headed up by Norwegian entrepreneur Christen Ager-Hanssen, has a 20% stake in Johnston and has been linked with a potential bid approach in the past.
US hedge funds were also said to be positioning themselves for a takeover last year after snapping up the company’s bonds at a discount.
Despite the rumoured interest, Johnston confirmed it is not in discussions with any potential suitors at the moment.
Shares rose 4.8% to 3.4p on Thursday morning.