The decision comes two days after WSU had to cancel Saturday's game against Stanford because it did not meet the 53-scholarship-player threshold needed to play, as a result of players in quarantine and isolation protocols related to COVID-19.
"As we work through the remainder of our schedule, we will continue to communicate with the Pac-12 Conference and UW if any scenario would emerge that would allow us to reschedule the game at a later point in the season," WSU athletic director Pat Chun said in a statement.
"This is so disappointing for our players, coaches and staff, as well as Husky Nation as we were all looking forward to the Boeing Apple Cup this week," Washington athletic director Jennifer Cohen said in a statement. "This is one of the best rivalries in college sports and every year we circle this game at the start of the season. We will work with Pac-12 to prioritize this game and look into any opportunities to play it should there be an open date for both schools down the road. ... We want to provide an opportunity for our football program to compete this weekend and are working to find another opponent."
Without an opponent this week, Washington, which had its season opener against Cal canceled, will attempt to find a replacement team to play. The Pac-12 announced this week that it will allow nonconference games, reversing a policy set earlier in the year.
Washington reached out to BYU about playing a replacement game this week, but the eighth-ranked Cougars resisted, sources told ESPN.
According to sources, BYU was concerned about agreeing to a game with Washington and then having the Pac-12 instead pair Washington with another league opponent -- possibly Utah on Sunday if Arizona State can't play again this week. If a Pac-12 opponent becomes available by the end of the day Thursday in any given week, the conference game must be played in lieu of a nonconference game.
BYU wanted a stronger guarantee before it agreed to the game and began preparations.
"We remain open to exploring options to add football games, and have been throughout the season," said BYU athletic director Tom Holmoe in a statement. "In that exploration process there are a variety of factors that need to be considered, including location, prep time for the game, the chances of the game being played, the testing protocols that are in place and what the game would do for our resume.
"At this point of the season, having played nine games and being nationally ranked, we are involved in discussions for possible matchups with other teams, on common open dates, for the benefit of both teams."
If neither Washington nor Washington State qualifies for the conference championship game, it is expected that the Pac-12 will try to arrange the Apple Cup for the weekend of Dec. 18-19.
ESPN senior writer Adam Rittenberg contributed to this report.