Dunn, who rushed for a team-high 1,140 yards last year, hurt his back during offseason workouts and had the surgery on Saturday. The team held off revealing the news while it dealt with the federal indictment of quarterback Michael Vick on charges related to dogfighting.

Vick, indicted last week, was barred from training camp by NFL commissioner Roger Goodell while the league looks into possible violations of its new personal conduct policy. Meanwhile, the Falcons have another major hole to fill during the preseason while Dunn recovers.

"I felt some discomfort in my back and legs that just never subsided," Dunn said in a statement released by the team. "After consulting with the medical staff, it was recommended that we have the surgery."

If the 32-year-old Dunn needs a full month to recover, he would miss all of training camp and the first two preseason games. But he should be back in time for the Sept. 9 opener at Minnesota.

Jerious Norwood, who rushed for 633 yards in his rookie season, will move up to the first team while Dunn is out.

"The doctors told me that the discomfort would have lingered throughout the 2007 season had we not had the surgery, so I felt like this was the best course of action for me," Dunn said. "I've had a tremendous offseason, and I feel great. I plan to come back stronger than ever and will do everything I can to help us get back to the playoffs."