Thompson (6-3, 292) entered the league as an undrafted free agent with the Indianapolis Colts on May 3. The Colts waived him on May 20.
Thompson played college football at Northwestern. He registered 91 tackles, 13 tackles for loss, six passes defensed, 5.5 sacks, and three forced fumbles in 51 games with 38 starts for the Wildcats. Thompson recorded 30 tackles, six tackles for loss, three sacks, three passes defensed, and two forced fumbles as a senior in 2018.
The announcement comes about 30 minutes before the 49ers take the field for their first practice of training camp.
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