Wall Street, grappling with mounting regulatory probes and investor claims over alleged interest-rate manipulation, may face yet another formidable foe: Itself.

Goldman Sachs Group Inc. and Morgan Stanley are among financial firms that may bring lawsuits against their biggest rivals as regulators on three continents examine whether other banks manipulated the London interbank offered rate, known as Libor, said Bradley Hintz, an analyst with Sanford C. Bernstein & Co. Even if Goldman Sachs and Morgan Stanley forgo claims on their own behalf, they oversee money-market funds that may be required to pursue restitution for injured clients, he said.

Because Libor is based on submissions from only some of the world's largest banks, the probes threaten to pit firms uninvolved in setting the rate against any implicated in its manipulation, Hintz said. Libor serves as a benchmark for at least $360 trillion in securities.