JPMorgan Chase & Co. says the money-market stress that sent short-term borrowing rates surging last month is likely to get much worse despite the Federal Reserve's attempts to inject billions of dollars into the financial system.

The Fed has offered overnight loans and started buying up to $60 billion of U.S. Treasury bills a month in an effort to ease pressure in the vast repo market, where banks typically lend their assets in exchange for short-term financing. Secured lending rates shot up in late September, with analysts pointing to scarcity of interbank reserves as well as regulations that limit the size of bank balance sheets and their repo-lending capacity as the potential culprits.

JPMorgan says it's not convinced the Fed has resolved the issues in the funding markets, according to a note from analysts led by Joshua Younger in New York. Funding pressures resurfaced last week even after primary dealers—firms approved to trade directly with the Fed—took all of the available overnight liquidity from the central bank and sold it as many T-bills as possible.