Boeing Co. is talking to a group of banks about a potential loan as it deals with the production halt of its grounded 737 Max jetliners, according to people familiar with the matter.

Citigroup Inc. is leading the discussions between Boeing and a small group of banks, said the people, who asked not to be named because the details are confidential. The precise structure and timing of the loan is in flux, but the financing may be an investment-grade term loan, they said.

Representatives for Citi and Boeing declined comment.

Boeing’s access to the credit markets could soon get more expensive. Moody’s Investors Service placed Boeing’s A3 senior unsecured debt rating on review for downgrade Monday, saying Boeing could face a “costly and protracted” recovery and “heightened operational and financial risk.” Any Moody’s action could give Boeing a rating in the lowest tier of investment-grade rankings. S&P Global Ratings cut the company to A-, the fourth-highest high-grade rank, in December.

The long-term grounding cost the company its title as the world’s largest plane-maker Tuesday after the number of jetliners it delivered in 2019 dropped to less than half of Airbus SE’s tally.

Boeing signed new revolving credit facilities totaling $9.5 billion (¥1 trillion) in October and almost doubled the size of its existing lender commitments. Investment-grade companies typically leave their revolvers undrawn to serve as a form of back-up liquidity, which is why Boeing might want another form of financing, one of the people said. The company could later decide to pay down any bank debt raised now with a future investment-grade bond sale, the person added.

The U.S. plane-maker faces growing financial strain as it reimburses customers, keeps suppliers afloat and maintains about 400 newly built Max jetliners that it can’t deliver until global regulators clear the jet to fly. Boeing is halting production of the 737 Max in mid-January, signaling that its emergence from the crisis will be lengthy.

The Wall Street Journal reported earlier this month that Boeing is examining plans to raise more debt to bolster its finances as the Max crisis continues. Boeing could raise as much as $5 billion, according to the Journal.