In an interview with TMZ Sports, Gatlin said it took him "months" to recover when he suffered frostbite on his feet and ankles as a result of cryotherapy in 2011:
Brown has not practiced since July 30, and ESPN received confirmation Wednesday that it was because of frostbite on his feet after he failed to wear proper footwear in a cryo chamber in France.
Gatlin added: "It was a disaster. I had, like, boils and blisters all over my ankles. ... Every day I had to get those blisters popped by hand by a therapist. ... It just got really, really bad."
The 37-year-old Gatlin is a five-time Olympic medalist, and he took gold in the 100-meter sprint at the 2004 Summer Olympics in Athens. He noted: "He's [Brown] not going to be able to run those routes properly without healing his feet totally."
Gatlin bounced back to compete in the 2012 Summer Games in London, and he won a bronze medal in the 100-meter dash with a personal-best 9.79-second run.
Brown only has a month before the start of the 2019 regular season, and the Raiders are counting on him to be an offensive difference-maker after acquiring him in a trade with the Pittsburgh Steelers.
The 31-year-old has been named a Pro Bowler in each of the past six seasons and seven times overall. He has at least 100 catches, 1,250 receiving yards and eight touchdowns in each of the past six campaigns as well.
Brown led the NFL with 15 touchdown receptions last season despite taking a backseat to JuJu Smith-Schuster at times, and he is expected to be quarterback Derek Carr's top target for the Raiders in 2019.
If Brown is out, Tyrell Williams will take over the top spot, with J.J. Nelson, Ryan Grant and rookie Hunter Renfrow also fighting for playing time.