Seattle Seahawks rookie receiver DK Metcalf needs knee surgery, but coach Pete Carroll expressed optimism that he won't be sidelined for long.

"DK's got an injury to his knee that we found after a couple days," Carroll told reporters Sunday night after the Seahawks' 25-19 preseason loss to the Vikings in Minneapolis. "It happened a few days back. So there's something. We're gonna do some work on it Tuesday and get him back in a hurry. So we're disappointed for him because he was off to a fantastic start, but I don't think this is gonna derail him for long. But he does have to have some work done, and we'll know more about that when we get back into town."

Carroll said doctors have said a quick recovery from surgery was expected after looking at the results of an MRI, though he did not provide specifics on the nature of the injury.

Carroll did say there was optimism that Metcalf could be ready for Week 1. Metcalf was with the team in Minneapolis but did not play against the Vikings after taking part in all of the practices that were open to the media this past week; Friday's practice was closed.

Rookie second-round pick Marquise Blair, who is vying for a starting job, left the game.

"He had back spasms in the second half," Carroll said. "So I don't know what that means, but he had a play and his back got tight, and it kept getting tighter and he couldn't go back."

Paxton Lynch, who is competing with Geno Smith to be Russell Wilson's backup, also left the game after taking a helmet-to-helmet hit from cornerback Holton Hill, who was ejected.

"He went through the [concussion] protocol, and he's still in there now," Carroll said. "He felt like he was OK, but he's still got to pass those tests, so we'll recognize all the process and take care of that."

Backup guard Demetrius Knox, an undrafted rookie, suffered what Carroll called a "nasty" quad injury.

Metcalf, whom the Seahawks chose with the final pick of the second round after trading up to No. 64, has been the most impressive of their 11-member draft class. He quickly caught on during the offseason program and has continued to stand out during training camp while regularly working with the No. 1 offense.

If Metcalf is unavailable for Seattle's Sept. 9 regular-season opener against the Bengals, Jaron Brown and David Moore would be the most likely candidates to start alongside No. 1 receiver Tyler Lockett.

The Seahawks are already without defensive end L.J. Collier, their first-round pick, because of a sprained ankle that could keep him sidelined for the rest of the preseason, if not longer. That means Seattle's top three picks this year -- Collier, Blair and Metcalf -- are all dealing with injuries.

Lynch replaced Wilson (6-of-9, 82 yards) on Seattle's third possession Sunday. He was 6-of-15 for 67 yards and a near interception while playing behind a shaky offensive line before Hill's hit sent him to the sideline. J.T. Barrett took over for the final four minutes and went 0 for 3 with an interception.

Seattle signed Barrett last week with Smith recovering from Aug. 9 surgery to remove a cyst in his knee. Smith did not play Sunday.

Vikings coach Mike Zimmer said he apologized to Carroll for Hill's hit on Lynch.

"No. 1, we don't want to see anybody get hurt, so I told Pete that after the game, sorry about his quarterback," Zimmer said. "No. 2, he can't drop his head. But saying that, when a quarterback is running an option, he ought to be fair game other than lowering your head and hitting him in the head. So if they're going to let these quarterbacks be runners, then we should be able to hit them. He didn't hit him legally, but we need to hit these guys."

ESPN's Courtney Cronin contributed to this report.