Warner said Monday he's having hard-to-describe issues with his eyes, a condition he had hoped would subside last week but never did. He said the Cardinals medical staff told him before Sunday's game he shouldn't play, and he agreed.
The decision ended Warner's string of 41 consecutive starts.
He suffered the concussion in the second quarter of Arizona's 21-13 victory at St. Louis and didn't play in the second half of that game.
Warner took all of the first-string reps in practice last week but acknowledged that the eye issue persisted.
"I just think I hoped that it would get better and better throughout the week, as we all did and were optimistic that it would be good enough to play," he said.
Warner tried to describe the symptom.
"It's not a visual issue where I'm foggy, where I can't see or I can't focus on something," he said, "but there's a fogginess that's kind of in and behind my eyes, or on top of my eyes. It's something that's just not right. It's just not normal."
He said he has unusual sensitivity to light, especially fluorescent light.
"Everything I look at there's kind of a shadow that kind of follows it that's different than normal," he said. "But this other feeling that I've tried to explain and nobody can really grasp what it is, I don't know if it's necessarily related to that light sensitivity."
"But again you've got to take it one day at a time," he said.
Warner said he was seeing the eye doctor "to see if we can come to any resolution if there's something related with the eyes or something there that we're not aware of."
Warner, who passed all the necessary neurological tests, said he was honest with the training staff and coach Ken Whisenhunt throughout the week as he experienced neck tightness as well as the eye problem.
"Then we got together again on Sunday morning and although the neck tightness was better, I was still having the issue with my eyes," he said. "That's when they said we don't feel comfortable with you playing, and I couldn't argue with them because I knew I wasn't right."
Warner's absence gave Matt Leinart his first start in more than two years. The former Heisman Trophy winner completed 21 of 31 passes for 220 yards with no interceptions. In the second half, he was 13 of 16 for 137 yards.
"I thought he did a great job," Warner said. "I thought he made some key throws in some critical situations. He did everything he needed to do to put us ahead with two minutes to go in the game."
Leinart directed a nine-play, 80-yard touchdown drive that put Arizona ahead 17-13 with 12:27 to play.
"Kurt had texted me something before the game, 'read and react,' and that's when you play your best, when you don't think about it, you don't think twice," Leinart said. "And that's what I did in the game, I read it and just played, and let my ability take over."
Leinart said he had about three hours to prepare once he knew he was starting.
"I'm hoping I probably get more reps this week just in certain situations, just so they have me more prepared," he said. "I don't know what's going to happen. Once again I'm going to assume Kurt's playing, but I'm going to prepare like I'm starting."
Whisenhunt defended the decision to give Warner his normal practice work as the starter last week, despite the chance that Leinart might get the job.
"Kurt wanted his reps. He was doing well," the coach said. "We felt like he was getting better every day. That's why we were preparing Kurt to play."