Hartsfield tried out for the Packers last season, but he wasn't signed to a contract.
The former All-Atlantic Coast Conference selection tore the anteior cruciate ligament in his left knee of his senior season two years ago.
"I'm feeling pretty good," Hartsfield said in March. "I'm feeling pretty confident in my ability to move on the field. Without a doubt, I can do everything."
He declined an invitation last year to the Cleveland Browns' minicamp on advice of his doctors, who told him it was too soon for him to start playing football again.
At 6 feet 2, 240 pounds, Hartsfield has the requisite size for an NFL linebacker. And he was extremely productive during four seasons in College Park, recording 338 career tackles, 27 for losses, 8.5 sacks, two interceptions, a forced fumble and a fumble recovery.
Hartsfield was leading the Terps with 78 tackles as a senior when he got hurt against Georgia Tech. A cut block from a fullback ended Hartsfield's college career.
"The timing was bad, obviously," Hartsfield said. "At the time, I was hearing I was going to be a late-round draft pick or better. Before I got hurt, I had invites to so many senior all-star games. I hadn't heard from the Senior Bowl, but I had heard from the East-West Shrine game and Texas vs. the Nation. It was rough on me."