Haynesworth was inactive for Sunday's loss to Indianapolis and has played in only three of six games this season.
Shanahan said Monday that Haynesworth was kept out of the game because the two-time All-Pro defensive lineman didn't have enough time to get back in shape after missing nearly a week following the death of a family member.
General manager Bruce Allen said over the weekend that Haynesworth won't be traded. Shanahan, who has final say over personnel matters, wouldn't go that far, telling reporters: "I just try to keep you guessing a little bit. You just never know. You just have to wait."