Pareto Securities cut its rating on the airline's stock, saying it was concerned about weak cash reserves and the risk that it may have to issue new shares to shore up its finances.
ABG Sundal Collier also cut its rating on the stock, from hold to sell, saying the firm was low on cash and in danger of breaching its loan covenants in the second quarter of 2020.
Norwegian Air said on Friday it had sold over two-thirds of its available seats for March and that the situation was "challenging" and "changing constantly".
Analysts have warned that Norwegian, which has expanded the low-cost carrier model to long-haul flights, could be particularly vulnerable due to its high debts.
ABG Sundal Collier forecasts Norwegian will have a cash balance at the end of the first quarter of 1.2 billion crowns and at the end of the second quarter of 0.9 billion crowns.
"Too low, in our view. This means we expect Norwegian to raise new equity," it said.
The airline has already raised 5.4 billion Norwegian crowns via three share issues in two years, as well as a convertible bond, to help shore up its finances.
The airline's shares hit a 15-year low on Friday, down 95% from their 2015 peak, and the company's market capitalisation is now 1.95 billion Norwegian crowns ($211 million).
Debts and liabilities amounted to 81.2 billion Norwegian crowns ($8.79 billion) at the end of 2019, while cash and cash equivalents stood at 3.1 billion crowns.
In 2018, Norwegian rebuffed takeover offers from British Airways' parent company IAG, which has since said it was no longer interested in buying the ailing carrier.
Norwegian's convertible bonds have so-called covenants linked to the finances of a key subsidiary, Arctic Aviation Assets (AAA), which must keep its book equity and debt levels within certain minimum levels.
ABG expects a book equity at the end of the first quarter of 1.56 billion crowns, just above the bond covenant of 1.5 billion crowns, unless the airline can make a profit from the planned sale of an aircraft.
At the end of the second quarter, "we see Norwegian Air breaching covenants on our numbers," ABG said.
Norwegian scrapped its 2020 earnings outlook and cut some transatlantic flights on Thursday, blaming the coronavirus outbreak.
At 1454 GMT, Norwegian Air's shares were down 23.7% at 12.06 Norwegian crowns ($1.30).
The stock has fallen almost 70% since the start of February, making it the hardest hit among European airlines, as the virus spread to Europe and the United States, forcing airlines to cut flights and costs and warn of a hit to earnings.
"There is clearly a risk for all the airlines, but we see Norwegian with a slim cash buffer perhaps at a (bigger) risk," Pareto Securities analyst Kenneth Sivertsen told Reuters, pointing out that it may require new equity.
He cut the stock to "hold" from "buy" and slashed its price target to 15 crowns from 50.
Norwegian Air hardest hit among European airlines: https://fingfx.thomsonreuters.com/gfx/buzzifr/15/8582/8582/Pasted%20Image.jpg
By Nerijus Adomaitis and Izabela Niemiec