If a sore knee sidelines Saints WR Adrian Arrington on Sunday, undrafted, unknown long shot Joe Morgan might be activated for his first NFL regular-season game.

Nothing new there. More than a third of the New Orleans roster –18 players –went undrafted out of college, and many of them play key roles.

Morgan, RB Travaris Cadet and DT Tyrunn Walker are the newest additions to the fold. The list includes RBs Pierre Thomas and Chris Ivory, QB Chase Daniel, FB Jed Collins, WR Lance Moore, C Brian de la Puente, DE Junior Galette, DT Tom Johnson, LBs David Hawthorne and Jonathan Casillas, CB Jabari Greer, S Rafael Bush, P Thomas Morstead, K Garrett Hartley and LS Justin Drescher.

These are no scrubs.

Thomas led the Saints in rushing last year. Ivory led them in rushing in 2010. Moore caught 79 passes in 2008, and scored eight TDs each of the past two years. Greer started every game in which he was healthy the past three years. De la Puente starts. Hawthorne will start if his knee is healthy enough on Sunday. Casillas, Galette and Johnson are slated for significant backup roles.

Five more New Orleans players were seventh-round picks, including WR Marques Colston (1,143 receiving yards in 2011), starting right tackle Zach Strief and LB Scott Shanle, entering his seventh year as a Saints starter.

“It’s a big key,” interim coach Aaron Kromer said. “When you think about a guy that has been picked in the seventh round or been a free agent or a practice squad player and has made the team, that guy might have more character or more desire because he was passed over by a lot of people.”

Morgan was thrilled just to make the Saints 53-player roster. He spent 2011 on injured reserve after ending his college career at tiny Walsh University.

“Right now to be even in consideration of being active is exciting,” he said. “If I’m actually active and get to play on Sunday, it’s going to be a dream come true and pretty emotional.”

It will not be unusual, though. If the Saints leave Morgan off the active roster, they might use Cadet, a rookie who has lined up in the slot at times in the preseason and caught a team-high 22 passes.

Morgan was last year’s free-agent find. Cadet, from Appalachian State, is this year’s.

“Look at this Cadet and what he has done in the preseason,” Kromer said. “You didn’t hear his name before he started practicing with us in any of the scouting world, and this guy came in and has done a wonderful job.”

Follow Saints reporter Guerry Smith on twitter @CBSSportsNFLNO.