"He didn't practice on Friday, he was sick," Shanahan said. "On Thursday, he didn't have one of his better practices and we weren't sure what the reason was. I'm guessing it was because he was sick.
"Without practicing Friday and Thursday not having one of his better practices, we kept him inactive."
But Haynesworth said after the 31-7 defeat he "was ready to play."
"They didn't really tell me anything," he said. "Haslett said I wasn't playing, so that's what we talked about in the hall. There was nothing heated or anything between me and Jim.
"If they choose to sit me, then they choose to sit me. This is their organization. I'm just a piece."
An expensive piece. Haynesworth signed a seven-year, $100 million free agent contract with Washington after the 2008 season. He struggled last season and has not been much of a factor this year, Shanahan's first as coach.
The Giants' Brandon Jacobs and Ahmad Bradshaw combined for 200 yards rushing and all four of New York's touchdowns. Haynesworth might have helped stymie some of New York's running game.
"You always want your best player playing at a high level," Shanahan said when asked if this would have been a particularly important game for Haynesworth to contribute.
Haynesworth has had a rocky relationship with Shanahan and his staff. There were differences over offseason workouts, conditioning tests and preseason playing time, but the crux of the issue was that Haynesworth didn't want to play nose tackle in a 3-4 defense.
On Sunday, he didn't play at all.
"We really don't pay too much attention to it," quarterback Donovan McNabb said. "Obviously, you guys will have a big story with it. It's something that runs on TV 24 hours. He's a brother of ours and he's in our locker room and we look to go to war with him.
"I didn't know much about the decision that was made until the beginning of the game when I saw him walking around in a sweat suit. The coach makes the decision. That's what we have to go by."
Copyright 2010 by The Associated Press