Monarch faces a race against the clock to secure fresh investment as the travel firm's operating licence is due to expire at midnight.
Last month the Civil Aviation Authority (CAA) granted a 12-day extension on the firm's Atol licence until 11.59pm on Wednesday.
That announcement was made just hours before the licence was previously due to expire.
Monarch responded by saying it had received "significant further investment" from shareholders and was "close to announcing the largest investment in its 48-year history" but no more updates have been issued.
Days earlier the company was forced to deny "negative speculation" that it is in financial trouble.
A further extension of the Atol licence is dependent on fresh funding.
The scheme compensates travellers in full and ensures they are not stranded if a holiday company collapses.
Monarch will be unable to sell package holidays from Thursday unless its licence is extended again or renewed.
Holidaymakers currently abroad or due to travel after that date would still be protected as the scheme is dependent on when a trip is booked rather than when it takes place.
The boss of Monarch pulled out of a public speaking engagement on Tuesday ahead of the deadline.
Andrew Swaffield, chief executive of Monarch Group, was scheduled to talk about the impact of Brexit at UK travel trade association Abta's annual convention in Abu Dhabi.
A spokesman for Monarch said Mr Swaffield missed the event as he had "business to attend to in the UK".
The CAA said there are no set criteria for approving Atol licence applications, but the process involves assessing a company's finances, business model, corporate governance and group structure.
The potential impact on consumers of an applicant going bust is also taken into account when extending a licence.