"Everybody evaluates their own situation as far as playing this game," the 23-year-old told the San Francisco Chronicle. "I've evaluated mine and I've decided I still want to play."
Reid later took to Twitter to walk back the statements he'd made to the newspaper about retiring, saying his words had been twisted.
The 2013 first-round pick out of LSU suffered two concussions in his rookie season with San Francisco. On Dec. 20 of last year, he sustained another during a game against the San Diego Chargers.
Reid didn't miss any playing time because of the first two incidents -- even though they happened in his first nine games as a pro. The third time, however, was different, though not for reasons one might expect.
Reid said held himself out of the regular-season finale, but only because San Francisco had been eliminated from the playoffs.
"I just decided it wasn't worth possibly getting another concussion for a game that wouldn't advance us," Reid said. "So I decided to sit that one out."
In March, linebacker Chris Borland, a 24-year-old up-and-coming star for the 49ers after a standout rookie season, announced he had decided to retire because he was worried about the long-term effects of brain injuries.
Borland never suffered a concussion in an NFL game, but said he believed he'd sustained one in training camp. Despite the injury, he said, he felt pressured to stay on the field and keep playing.
Last week, 25-year-old 49ers right tackle Anthony Davis announced that he would also be stepping away from the NFL after a head injury put him on the sidelines for four games last season. But Davis, a five-year pro, said he hopes he'll be able to return to the field.
"After a few years of thought, I've decided it will be best for me to take a year or so away from the NFL," Davis said in a statement. "This will be a time for me to allow my Brain and Body a chance to heal. I know many won't understand my decision, that's ok."
Reid said he respected Borland and Davis for drawing a line and saying what they were willing to live with. So what would it take for Reid to declare he'd had enough?
"I'm not putting a number to it," he said. "I will continue to evaluate my own situation. If I have another concussion and I don't feel like I can play anymore, then I won't ... If I feel that I still can play, then I will. It's just a case-by-case basis.
"I know it's a huge deal right now in the NFL, and everything is being put under a microscope, but that's how every injury is. It could be a dislocated shoulder. You evaluate your situation and see if you're healthy enough to still play."
Follow Matt Wilhalme on Twitter @mattwilhalme