Singleton is Penn State's leading rusher with 53 carries, 408 yards, and three touchdowns.
"We are investing a lot of time in it, and we understand how important it is."
Warren broke the program record for most touchdowns by a tight end, while Clifford had his first career 100-yard game.
Singleton was noticeably absent from practice on Wednesday.
Washington has made a name for himself on defense and special teams this season.
