The Chiefs can activate them from PUP as soon as they pass a physical.
Thornhill tore an anterior cruciate ligament in Week 17 against the Chargers. He underwent surgery Jan. 14.
He finished the year with 56 tackles, five pass breakups and three interceptions.
Rankin, 25, injured his patella in a November game and finished the season on injured reserve. He played six games with five starts last season.
Rankin played for Houston in 2018, appearing in all 16 games with four starts.