Porter is hoping to get medical clearance to play Sunday night against the New Orleans Saints, his former team.
Porter, who had no history of seizures, wasn't allowed to fly to the Broncos' last game, at San Diego on Oct. 15, after he began experiencing light headedness and a racing heart -- similar to the symptoms he felt before his seizure, team spokesman Patrick Smyth said.
Smyth emphasized Porter didn't suffer a second seizure but was left back in Denver as a precaution. Porter returned to practice on a limited basis this week.
Porter, whose seizure was first reported by the Denver Post on its website Thursday afternoon, wasn't in the locker room during the 45-minute media access period Thursday but later tweeted, "I would like to thank EVERYONE for the prayers and wishes. It really means a lot to me."
The last time Peyton Manning and Drew Brees squared off, in the 2010 Super Bowl, it was Porter who stole the spotlight, returning an interception 74 yards to seal the Saints' 31-17 win over the Indianapolis Colts.
Porter had sidestepped questions about the nature of his illness earlier this week.
He also said earlier this week that he was eager to face his former teammates and optimistic he'd be cleared to play.
Porter, who was lifting weights with former Saints teammate Jeremy Shockey when Shockey had a seizure in May 2010, suffered his seizure in mid-August and was held out of a preseason game against Seattle that week. The cause of the seizure was undetermined and he returned to the field the following week.
Porter had a monster debut for Denver in the season opener, breaking up five passes, collecting eight solo tackles and returning an interception for a touchdown that sealed the Broncos' 31-19 win over Pittsburgh -- his NFL-leading third career game-sealing score since 2009. That performance earned him AFC Defensive Player of the Week honors.
He hadn't had any more symptoms until two weeks ago while preparing to leave for San Diego.
Porter returned to practice Monday for non-contact work following the Broncos' bye.
Asked if Porter's condition had worsened, coach John Fox noted Porter was "limited" Wednesday and then was absent Thursday, so "you fill in the blanks."
"Right now, Tracy is being evaluated," Fox said. "When he's cleared to physically be able to practice, he'll be out there. I don't know all the symptoms. When we figure out how to deal with the illness, then he'll be out here."
Champ Bailey said he was concerned about his fellow cornerback "because it's a question mark. You don't really know what's going on. I try to help all the young players here, but in this situation, there's not much I can do. But we're all praying for him and hopefully he'll be back sooner rather than later."
Safety David Bruton, whose locker is next to Porter's, said his teammates just want him healthy even if that means missing more games.
"That's one of our brothers. We're not just here as co-workers, we've built a friendship, a bond and we care about each other, so it extends beyond football," Bruton said. "We care for him and wish him the best and we'd love to have him back with us some way, somehow."
That said, "it depends on how he feels and how the doctors feel," Bruton added. "It's not our say. If he can go, that's great. If not, Chris and T.C. both stepped up big the last time when Tracy couldn't go."
Chris Harris collected two interceptions at San Diego and Tony Carter picked off another pass as the Broncos overcame a 24-0 deficit for a 35-24 win that put them in a tie with the Chargers atop the AFC West at 3-3.
On Monday, Porter said he was his backups' biggest cheerleader two weeks ago.
"I was jumping up off the couch when those guys intercepted the ball. I wanted to be a part of it, but those guys are my teammates so I'm not mad that they did it and I didn't," Porter said.
Porter signed a one-year, $4 million free agent deal last spring with the Broncos, where he's trying to help Manning secure that second Super Bowl title that he denied him on Feb. 7, 2010, with his big play.
Now, he's hankering for a chance to pick off Brees.
"It will be great to intercept Drew, to make him mad and put my team closer to a victory," Porter said. "But I still have to be in the right place at the right time like I was in the Super Bowl."
In comments on a conference call before the nature of Porter's illness became public, Brees said it will be strange seeing Porter in a different uniform.
"I had four great years with Tracy, going against him in practice every day," Brees said. "You know, he obviously was a big part of what we were able to accomplish here the last four years and it's always weird to see a guy like that who was such a big part of what you did and all of a sudden he's on the other side in a game."
With the league's worst defense -- they've allowed 2,793 yards over the first six games, most since 1950, the Saints (2-4) miss Porter's presence in their defensive backfield.
"Tracy plays the deep ball better than any corner I've seen," Saints safety Roman Harper said. "He can run. He's very physical at the line and he's very smart. He's a very confident player. I love the dude to death. I know he misses us, and we miss him, too."