For the first time this season, Cougars coach Ken Bone did not start the sophomore who entered Saturday sixth in the nation in scoring at 22.3 points per game.
A school spokesperson said Thompson was late Friday for the team's bus ride that began its trip to Seattle. He had started his first 53 games at WSU.
Freshman Xavier Thames started in place of Thompson.
Bone, a former assistant of Lorenzo Romar at Washington, has benched other starters for being late during his first season at WSU.