The F.B.I. is investigating whether the assistant at Rutgers who first voiced concerns about the abusive behavior of his boss, Mike Rice, tried to extort the university.

As part of its investigation, an F.B.I. agent recently visited the office of Tim Pernetti, the athletic director, according to two people familiar with the investigation, one of whom is a university official who insisted on anonymity because he was not authorized to speak publicly. Pernetti resigned as the Rutgers athletic director on Friday.

In December, a lawyer representing the former assistant, Eric Murdock, a retired N.B.A. player, sent a letter to the university demanding $950,000, according to a copy of the letter. The letter — which was first reported by ESPN on Friday — was sent two weeks after Rice was suspended for three games for the abusive behavior that eventually led to his firing Wednesday.

The university declined to pay the money demanded in the letter, and Murdock eventually publicized video footage that showed Rice kicking his players, throwing basketballs at them and taunting them with homophobic slurs. The footage has touched off a scandal that has led to the resignations or dismissals of at least four Rutgers officials.