Stevens, who signed with the Bucs in April 2007 after spending his first five NFL seasons with the Seattle Seahawks, had 18 receptions for 189 yards and four touchdowns in 15 games last season.
Gradkowski was a sixth-round draft choice in 2006 out of Toledo. He started 11 games as a rookie after Chris Simms was lost to a season-ending spleen injury, throwing for 1,661 yards, nine TDs and nine interceptions.
As the No. 3 quarterback in 2007, he appeared in four games and was 13-of-24 for 130 yards, no touchdowns and one interception.
The move leaves five quarterbacks on the roster -- Jeff Garcia, Brian Griese, Luke McCown, Simms and rookie Josh Johnson. A sixth, Jake Plummer, is under contract but has said he is retired.
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