Nine-time Pro Bowl left tackle Walter Jones left Seahawks practice early on Monday with an apparent back injury.

The 35-year-old linchpin to Seattle's offensive line for the past decade was practicing for the third time since training camp began July 31. He took part in one series with the starting offense, then left the field in pain.

He stood and kneeled next to a trainer while wincing and holding his back for a few moments. He eventually summoned the trainer to escort him into team headquarters.

Jones practiced on the first day of camp, then sat out each practice until last Thursday because of back spasms. He said upon his return to the field last week that he had tried to do too much too soon in that initial practice.

Coach Jim Mora wasn't entirely sure what was aching Jones this time, at least not immediately after practice.

"(Trainers) just said, 'Hey, we're taking Walt in. He's not feeling right,'" Mora said.

Jones has missed time in Seahawks training camp before because of contract issues. But this time he is coming off microfracture knee surgery and is learning the new zone-blocking scheme of first-year offensive coordinator Greg Knapp.

For now, usual right tackle Sean Locklear is replacing Jones at left tackle. Ray Willis is at right tackle.

Knapp and Mora have said repeatedly this month how important solving the "puzzle" of who will play where on the offensive line is to getting off to a good start this season for a team that fell to 4-12 in 2008. Seattle opens on Sept. 13 against division-rival St. Louis.

Asked Monday when he needs to see his entire starting line healthy and practicing together, Mora said with a laugh: "Wednesday before the Ram game."

Knapp said he isn't worried, either, about Jones' August aches.

"I would like him to (practice) because I've never worked with him," said Knapp, who spent last season as Oakland's offensive coordinator. "But I've been told by many people in the building here, 'Don't worry. You don't have to worry about Walt.'

"The limited snaps you do see him, you go, 'Wow!'"