The Bucs released rookie defensive end Maurice Evans on Saturday to make roster room for Jackson.
The Bucs could have held out Jackson for one game under the exemption but decided they needed him to help their struggling secondary. Tampa Bay lost eight-year veteran Jermaine Phillips for the season with a broken thumb and has given up six pass plays of 40-plus yards -- five of them for touchdowns.
The NFL suspended Jackson for the first four games of the season for violating its substance-abuse policy. It was a big blow for the Bucs because Jackson is the only defensive player in franchise history to start in every game in his first two seasons.
Will Allen has started at free safety in Jackson's absence. Whenever Jackson is ready to start, Allen likely will return to a reserve role and Sabby Piscitelli will remain at strong safety.
Jackson apologized to his teammates before serving his suspension and came back this week with a new outlook.
"I could sit here and go on forever as to how much I learned (from being suspended)," Jackson said. "The main thing is that this is what I love to do, this is what I'm blessed to do. I definitely felt I let my team down. ... I disappointed myself, but your actions affect others around you, and that's one thing that hit home."
The Associated Press contributed to this report.