Jay Glazer of Fox Sports revealed the investigation Sunday.
Glazer's report said a line judge saw a San Diego equipment manager hiding an illegal sticky substance and giving it to players. The judge confiscated the substance and sent it to officials of the team and the National Football League, the report said.
NFL.com described the material as a "Stickum-type" substance.
Stickum and other sticky subtances once used by receivers and some other players to help them catch footballs were banned by the league more than three decades ago, an item in Wikipedia said.
The NFL had begun an investigation of the Chargers before the Oct. 15 game, Glazer said.
NFL spokesman Greg Aiello said the league was still gathering facts. The Chargers said in a statement they were cooperating fully with the investigation.
The Chargers lost the game 35-24.