Greenlaw (Achilles) is active for Thursday Night Football against the Rams, Lindsey Pallares of the 49ers' official site reports.
The linebacker was activated from the reserve/PUP list earlier in the day Thursday after putting in a full practice Wednesday. Greenlaw topped the 100-tackle mark in each of the last two campaigns before tearing his left Achilles while running back onto the field during Super Bowl LVIII back in February. The injury was serious enough to keep him out until the middle of December, so it's unclear how much Greenlaw will play Thursday.