Steelers physician Dr. Anthony Yates said that Maddox has a cerebral concussion and a spinal cord concussion, not a contusion, as was reported Sunday.
Maddox underwent an MRI, CT scan and X-rays that all showed no structural damage. Yates said Maddox has a headache, but otherwise is doing well.
"Tommy is doing much better now," Yates said. "We are certainly happy with his progress. His official diagnosis is a brain, or cerebral concussion, and a spinal concussion, not a contusion. This is important in future management and future prognosis."
Yates said that Maddox will be hospitalized upon his return to Pittsburgh and be monitored by Dr. Joseph Maroon, the team's neurologist. Yates also said that it is too early to speculate on the future of Maddox' playing career.
"It's good news and I think everybody is pleased with the progress," said Steelers Vice President Art Rooney II. "It's a good situation he is up walking this morning. So far, so good."
Maddox was injured in Sunday's 31-23 loss to the Titans after being hit by linebacker Keith Bulluck. He lost feeling in his extremities, but later regained feeling at a Tennessee hospital.
He was taken off the field by ambulance and hospitalized after suffering the injury on the final play of the third quarter.
Team trainers and doctors spent at least 10 minutes tending to Maddox, who was motionless as he was strapped to a backboard.
Maddox was then loaded into an ambulance on the field and taken to Baptist Hospital, where he remained overnight.
He was falling forward as he completed a pass to rookie Antwaan Randle El when Bulluck put his forearm into the quarterback's left shoulder.
Maddox, a first-round pick in 1992 out of UCLA, who revived his career in the Arena League and XFL, was responsible for all of Pittsburgh's five wins after replacing an ineffective Kordell Stewart in a Sept. 29 overtime win over Cleveland.
Last week, after throwing for a career-high 473 yards last week in a tie against Atlanta, Maddox threw for just 194 yards and was intercepted three times before he was injured.
Maddox, 31, entered Sunday's game as the AFC's second-highest ranked passer with a quarterback rating of 97.9.
After three years out of football, he starred in the Arena League in 2000 and the XFL in 2001, winning MVP honors in the now-defunct league before signing with the Steelers last year.
The Steelers (5-4-1) are in first place in the AFC North, one-half game ahead of Cleveland.