The Redskins also signed defensive end Frank Kearse on Monday.
Amerson was the 51st overall pick two years ago and started 15 games last season for the Redskins, but he was limited to special teams duty in Washington's 24-10 victory over the St. Louis Rams on Sunday.
Coach Jay Gruden says Amerson ''was just the odd man out, unfortunately'' in a defensive backfield that will get cornerback Chris Culliver back this week after serving a one-game suspension Sunday.
The Redskins (1-1) play at the New York Giants (0-2) on Thursday night.
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