A source informed of the decision confirmed the move to PFT late Tuesday night.
Willson spent the first five seasons of his career with the Seahawks after being a fifth-round pick out of Rice in 2013. Willson appeared in 72 games for Seattle over that span with 37 starts. He caught 89 passes for 1,129 yards and 11 touchdowns during his five years in Seattle.
Willson spent last season with the Detroit Lions, catching just 13 passes for 87 yards in 14 games. He signed with the Oakland Raiders this offseason before being released at the end of training camp.
Seattle traded Vannett to the Steelers on Tuesday in exchange for a 2020 fifth-round draft pick.
Vannett was in the final year of his rookie deal with Seattle after being a third-round pick in 2016. He’s appeared in 42 games with 16 starts for the team with 48 catches for 463 yards and four touchdowns. He had caught four passes for 38 yards in three games for Seattle this season.