Smith confirmed the injury in a text message to ESPN's Ed Werder. Smith also told Werder that renowned surgeon James Andrews will perform the operation on his knee.
Smith's season-ending injury was reported earlier Monday by Pro Football Talk. He suffered the injury in Sunday's preseason game against the Houston Texans.
A 10-year veteran who is shifting to outside linebacker in first-year defensive coordinator Rob Ryan's 3-4 scheme, Smith told Werder he was ready to transition from his customary position of defensive end.
"It was going well," Smith said in his text to Werder. "The transition wasn't that bad. Rob had me in a great position to do well this year, [and] I'm disappointed I won't be able to help my team out."
Smith was a projected starter, as was fellow outside linebacker Victor Butler, who also is recovering from knee surgery that will sideline him most or all of the season. The 32-year-old Smith had six sacks last season and has 67.5 sacks in 139 career games, all with the Saints.
Information from ESPN's Ed Werder and The Associated Press was used in this report.