He knew something wasn't right. He had just played 73 snaps and made 11 tackles in Arizona's 24-20 win over the Philadelphia Eagles, but he couldn't recall much, if any, of it.
"I don't really remember the game," Jefferson said. "I just remember when I started driving ... I just stopped for 30 minutes. I was like, 'What just happened?' I don't remember what happened. It was kinda scary.
"I went home and watched the film on the iPad. It was like seeing you on auto pilot. It was pretty weird."
But he remembered how many tackles he had.
"I might have to push auto pilot a couple more times," Jefferson said jokingly.
Jefferson was diagnosed with a concussion Monday morning. He passed the concussion protocol on Thursday and practiced in a limited role, working on kickoff coverage during the open portion of practice.
He thinks it happened on a kickoff, but Jefferson said he wasn't sure when he talked to the media Thursday.
Defensive coordinator Todd Bowles hopes he'll have Jefferson for Sunday's showdown against the Dallas Cowboyss, but added that "concussions are a funny thing."
As for Jefferson, he doesn't want to rush back.
"This is your brain you're talking about," he said. "You don't want to do anything like that. I'm just going to see what they say but I feel fine.
"We got a long season ahead of us; I don't want to rush back."