Head coach Sean Payton said Pressley, who practiced as recently as Saturday, was increasingly bothered by an old right foot fracture that had never healed properly. Pressley will have surgery to repair it, the coach said.
"We tried to manage it a little bit and it was still becoming problematic," Payton said. "We think the injury is something that can heal with the proper procedure. We just chose to have it done right now rather than wait and try to treat it. It's just gotten progressively worse. ... It became apparent it was going to stay aggravated if he stayed on it."
Pressley, who is 6-foot-3, 301-pounds, was the first of the team's two fifth-round selections, taken 144th overall out of North Carolina State.
Placing Pressley on injured reserve opened a roster spot, which the Saints filled by signing free agent defensive end Marquies Gunn.
Gunn spent parts of 2007 on the practice squads of the New York Giants and Tampa Bay Buccaneers.