Washington's absence is not related to his pending court case in California on two charges, including a felony, of allegedly sending a video of his ex-girlfriend, who was then 15, participating in what she described in a report by NBC Bay Area as non-consensual sexual acts.
Frost told reporters that Washington, who ranks third on the team in rushing (298 yards on 50 carries) and has appeared in the first seven games, likely isn't part of the team's plans "in the immediate future."
Washington hasn't practiced with the team since Nebraska's Oct. 12 loss at Minnesota.
"There's certain standards that we ask our players to uphold," Frost said Monday. "When those standards aren't upheld, it doesn't matter who it is, they're not going to be a part of our plans that week or potentially longer."
On Thursday, Frost said he plans to speak with Washington about a possible return but said the running back must do "a lot of things to earn his team's trust back and our trust back."
Frost didn't say Washington is suspended and thinks Washington remains enrolled at the university. A university spokeswoman told The Associated Press that Washington remained enrolled as of Monday afternoon.
Washington will next appear in court on Dec. 12. Frost has said Nebraska wouldn't consider any additional discipline for Washington until the case is resolved.