Haynesworth underwent an MRI Thursday after complaining of soreness in the knee during the past week.
Coach Mike Shanahan has required Haynesworth to pass the team's conditioning test before taking part in training camp workouts, but Haynesworth has been unable to complete the series of running drills in the allotted amount of time.
He failed the test twice last week and has not attempted to pass it since then because of the knee soreness.
"His knee has been a little bit more sore than it has been in the past," Shanahan said on the Washington Web site Thursday. "This (the test) was just a preventative measure to see if he's all right. Then we'll go through the rehab work to get him stronger."
Haynesworth had four sacks in 12 games last season, his first for the Redskins after playing seven years with Tennessee.
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