Analysts at JPMorgan and Citi said in research notes that Banco Bradesco SA had the largest nominal exposure to the firm, while Banco BTG Pactual SA topped exposure as a proportion of loans.

Americanas revealed last week almost $4 billion in "accounting inconsistencies." Its chief executive and chief financial officer resigned. Shares of the retailer have plunged nearly 80% so far this year.

Americanas could be liable to repay up to 40 billion reais ($7.81 billion) in debt earlier than planned, and a judge set a 30-day deadline for it to file for a potential bankruptcy protection.

On Saturday, BTG filed an appeal of a decision that protected Americanas from creditors, attacking the retailer's shareholders, a trio of Brazilian billionaires and founders of 3G Capital.

Considering JPMorgan's and Citi's estimates, BTG had a 1.9 billion-real exposure to Americanas, which was seen accounting for roughly 1.5% of its loans, while Bradesco had exposure of 4.7 billion reais, or 0.5% of loans.

Banco Santander Brasil SA, the local unit of Spain's Banco Santander, had 3.7 billion reais in exposure, or about 0.6% of loans.

"We find that the impact of our coverage could range from 1% to 7% in net income and from 0.1% to 1% in terms of equity," Citi said, noting that Santander Brasil, BTG and Bradesco would be the most affected in both accounts.

Sergio Rial, the outgoing Americanas chief executive who uncovered the accounting inconsistencies, is a former head of Santander Brasil, where he still serves as chairman of the board.

"Based on past corporate cases in Brazil, we believe banks should start provisioning for about 30% of it, which may eventually increase depending on Chapter 11 outcome," JPMorgan said.

Shares in BTG were down more than 4% on Monday, while Santander Brasil and Bradesco dropped more than 3% each, compared with a 1.7% fall in Brazil's benchmark stock index Bovespa.

Americanas shares plummeted by 41.6% to 1.84 real on Monday, following a 77.33% drop on Thursday.

Moody's cut the retailer's rating to "Caa3," placing it under review for a further downgrade, and a second industry group filed a lawsuit against the firm in Rio de Janeiro.

The Instituto da Cidadania, which represents citizens and consumers, said in an initial affidavit that the company acted in bad faith, "given the defendant's attitude of filing false financial statements."

Americanas declined to comment.

An industry group representing investors is also suing the retailer.

"The scenario remains adverse for the company and we continue to recommend exiting its assets," Guide Investimentos analyst Gabriel Araujo Gracia said in a research note, citing the high level of uncertainty surrounding the case. "The story seems far from over."

($1 = 5.1248 reais)

(Reporting by Tatiana Bautzer and Gabriel Araujo; editing by Jason Neely, Alistair Bell and Leslie Adler)

By Tatiana Bautzer and Gabriel Araujo