TAMPA, Fla. — Vincent Jackson had a growing family, a flush bank account from his sterling 12-year N.F.L. playing career and a thriving portfolio of business investments to keep him busy. Intelligent, active, philanthropic and eager to please, he was popular in the Tampa Bay area, where he and his family moved in 2012 when he joined the Buccaneers.

Jackson, it seemed, was an N.F.L. role model, until he was found dead and alone in a hotel room at age 38 in February, just days after his former team won the Super Bowl. Until then, Jackson had hidden his alcoholism and declining cognitive health from the public. Those conditions, though, had accelerated during the pandemic, which had derailed his business and pushed him into isolation.

According to the Hillsborough County Sheriff’s Office, Jackson was found dead on Feb. 15 at the Homewood Suites in Brandon, Fla., a few miles east of Tampa, where hotel staff members said he had been staying since Jan. 11. A cause of death was not announced by the Hillsborough County medical examiner’s office.

Now the Jackson family has at least one clue to his demise: a diagnosis of chronic traumatic encephalopathy. Doctors at the C.T.E. Center at Boston University have determined that Jackson had a “mild” form of the disease, which is associated with repeated hits to the head. C.T.E. has an array of symptoms, including memory loss, trouble managing daily chores and mood swings, which Jackson’s wife, Lindsey, said he exhibited with growing frequency in and after the 2016 N.F.L. season, his final one.

“His whole plan in the N.F.L. was to set himself up to not have these struggles,” Lindsey Jackson said in an interview at her Tampa home. He had done everything to set up a graceful retirement from football, she said, adding, “It’s not the ending he wanted.”

The C.T.E. diagnosis will provide only a partial coda for Lindsey Jackson and their four children. Though the family has come to grips with his absence in the 10 months since his death, many questions will never be answered. C.T.E. can only be diagnosed posthumously, so the Jacksons are left to piece together what was going on in his brain during the final years of his life.

Jackson was a three-time Pro Bowl wide receiver and had six seasons with more than 1,000 yards receiving. Protective of his image, Lindsey Jackson said she had been reluctant to speak about his struggles. But she agreed to her first interview since his death, she said, to help the families of other former players spot and seek treatment for C.T.E.’s effects.

“I think the message is, if you played for a long time and you’re experiencing symptoms, it’s very likely that this is what it is,” she said this month from her husband’s “man cave,” where five televisions, a wet bar and a Christmas tree decorated the room. “I didn’t know that; Vincent didn’t know that. We thought it was just concussions, and we’d love for people to realize it’s more than that.”

She said they sometimes discussed the dangers football presented, notably after he saw “Concussion,” the 2015 movie about Dr. Bennet Omalu, who first diagnosed C.T.E. in former N.F.L. players. Vincent Jackson had read studies that showed football players’ risk of severe cognitive decline later in life was associated with the length of their careers. He refused to allow their children to play tackle football until they reached high school. (Two of the Jackson children play flag football.)

“When I look back at the different conversations we’ve had, I feel like he probably knew that there was something going on without actually vocalizing it,” Lindsey Jackson said.

Vincent Jackson grew up in a military family and had a reputation for outworking other players. Teammates nicknamed him Invincible, and he took pride in never making excuses or showing weakness. He shrugged off concerns about brain injury by saying he did not absorb many helmet-to-helmet hits because he played wide receiver. He noted that he never had a diagnosed concussion.

“I was fortunate, trust me,” Jackson told the alumni magazine from the University of Northern Colorado, his alma mater, in 2018.

Diagnosed concussions, however, are not reliable indicators of C.T.E. Only about 20 percent of people found to have C.T.E. had a diagnosed concussion, according to doctors at the C.T.E. Center at Boston University, who analyzed Jackson’s brain.

A more direct association are the thousands of smaller, subconcussive hits that Jackson would have absorbed in his two decades of practices and games. Players cope with these hits in any number of ways — painkillers, recreational or medical marijuana and other treatments. According to his widow, Vincent Jackson’s relief was alcohol. Late in his career, she said, he told her that his brain “felt fuzzy” at times and that alcohol cleared it up.

Dr. Ann McKee, the professor of neurology and pathology at Boston University School of Medicine who diagnosed Jackson’s C.T.E., described the damage to his brain in clinical terms. It had “mild frontal lobe atrophy” and a “split in the internal membrane” that could be from the trauma of playing football, she said. There were multiple lesions, mostly in the frontal cortex of his brain.

McKee and Lindsey Jackson put that damage into everyday terms. She said that, beginning with his final year in the N.F.L., her husband began to forget conversations. He showed symptoms of depression for about six months after leaving the league, and without the structure of the football season, he no longer had to temper his drinking. By 2018, when he was 35, his attention span had diminished and he had difficulty solving problems. She said he became paranoid, shutting the blinds when he was home.

Like many former professional athletes, Jackson also grappled with the emotional torment of leaving one life filled with euphoric highs and bruising lows every Sunday for another, more sedate existence with time to stew over unresolved aspirations.

While he made the playoffs four times with the San Diego Chargers, he never played in a Super Bowl, and the Buccaneers never made the postseason and had only one winning season during his five-season tenure with Tampa Bay.

During his playing days, Jackson learned painfully that he was expendable. A huge image of him reaching to make a catch hung on a banner outside Raymond James Stadium, the Buccaneers’ home, after his arrival in 2012. When injuries reduced his playing time, the banner was taken down, a gut punch for the player.

“It’s a business, and it hurts,” Lindsey Jackson said. “It’s hard for anyone to deal with, I think.”

After his contract with the Buccaneers ended after the 2016 season, he threw himself, as he had planned, into his restaurants, real estate ventures and philanthropy, including his Jackson in Action 83 Foundation, which provides emotional and educational support for children in military families. But like many players, he had a tough time adapting to a life without the brotherhood of the team.

“You can prepare to have another career and make money another way, but nothing ever matches that,” said Randy Grimes, who played nine pro seasons, all with the Buccaneers, left the N.F.L. with an addiction to painkillers and now helps former athletes with substance abuse issues at WhiteSands Treatment Center in the Tampa Bay area.

The pandemic, though, altered Jackson’s routines drastically. He fretted about having to lay off workers. Business meetings were virtual, diluting one of his favorite activities, networking. At home most of the day, there were fewer barriers to grabbing a drink.

The success of his former team, the Buccaneers, who won the Super Bowl the week before he died, was both a source of joy and remorse. The team’s championship had reminded him of the losing seasons he had endured with the team, Lindsey Jackson said.

When it became obvious to even his children that he did not have his drinking under control, she said, he moved into a hotel about 20 minutes away.

After Vincent Jackson stopped responding to family members, they asked law enforcement on Feb. 10 for help locating him. Two days later, sheriff’s officers found him at the hotel, and “after assessing Jackson’s well-being,” they canceled the missing person’s case. Three days after that, a housekeeper found Jackson dead in his room.

Lindsey Jackson has gone back to work as a first-grade teacher, and their four children, ages 3 to 8, sprint around the house. Family have stepped in to help, including Lindsey’s two sisters and Vincent’s parents.

Ornaments dangle from the Christmas tree in the man cave: ceramic disks with photos of Lindsey, Vincent and their children alongside little footballs and football helmets.