METAIRIE, La. -- Left tackle Terron Armstead is one of four New Orleans Saints players who will start training camp on the physically unable to perform list. But a source indicated that the injury is not significant, so Armstead shouldn’t miss much time.

UPDATE: Another source said Armstead is dealing with a soft-tissue injury and should return within a couple weeks.

The other players on the PUP list are cornerback Keenan Lewis (hip), defensive end Hau'oli Kikaha (knee) and receiver Vincent Brown (unknown). The Saints’ first practice is Thursday in West Virginia.

The Saints are being cautious with Terron Armstead, who suffered a significant knee injury last year. Joe Robbins/Getty Images

Players can come off the PUP list at any time. But teams officially designate them on that list if they aren’t ready to practice on Day 1. The only way a player can begin the regular season on the PUP list is if he is placed on the list before training camp and never returns to practice.

Armstead’s injury is unknown. He battled a significant knee injury last year but participated for most of OTAs and minicamp this summer. Losing him for any regular-season games would be a huge blow for the Saints, since he has emerged as one of the best young offensive linemen in the NFL. But it doesn’t sound like that’s a concern.

Lewis also participated in OTAs and minicamp on a limited basis while recovering from last year’s hip injury. He said this past weekend that he is healthy but expects to be limited to start camp as a precaution. His last surgery was in January.

Kikaha is expected to miss all or most of the season with an ACL injury he suffered during OTAs. The PUP list designation gives him an opportunity to return later in the season, but there is no indication whether he might be healthy enough to do so.

Also notable is the fact that safety Jairus Byrd is not on the PUP list, which means he might start out training camp healthy for the first time in his three years with the Saints. Byrd did not participate in team drills during OTAs and minicamp while rehabbing the knee injury that he has been dealing with for the past two years. But coach Sean Payton said earlier this summer that Byrd was expected to return for training camp.