Grant Wahl, one of the best known football writers in the United States, died early Saturday while covering the World Cup match between Argentina and the Netherlands.
US media seated near him said Mr Wahl fell back in his seat in the media tribune at Lusail Iconic Stadium during extra time and reporters adjacent to him called for assistance.
Emergency services workers responded very quickly but it was later confirmed that the journalist had died.
Wahl was covering his eighth World Cup and wrote on Monday that he had visited a hospital while in Qatar as he was feeling unwell.
And his brother Eric Wahl, who is gay, believes that the journalist could have been killed as he had been "healthy" and had "received death threats".
Grant had been stopped briefly by security, as he tried to enter the stadium for the US vs Wales group game, because he was wearing a rainbow shirt.
His brother Eric said through tears on Instagram: "I am Grant Wahl’s brother I am gay I am the reason he wore the rainbow shirt to the World Cup.
"My brother was healthy, he told me he received death threats, I do not believe my brother just died, I believe he was killed and I just beg for any help."
Grant had earlier written about feeling unwell: "My body finally broke down on me. Three weeks of little sleep, high stress and lots of work can do that to you.
"What had been a cold over the last 10 days turned into something more severe on the night of the USA-Netherlands game, and I could feel my upper chest take on a new level of pressure and discomfort.
"I didn't have Covid (I test regularly here), but I went into the medical clinic at the main media center today, and they said I probably have bronchitis. They gave me a course of antibiotics and some heavy-duty cough syrup, and I'm already feeling a bit better just a few hours later. But still: No bueno."
During the World Cup, Wahl drew international attention after saying he was briefly stopped from attending the US match against Wales on November 21 over wearing a rainbow-coloured T-shirt.
Rainbow-colored armbands, shirts and other items have been a focus of attention during the tournament in part over Qatar's stance on LGBTQ rights. Gay and lesbian sex is criminalised in Qatar, a conservative Muslim nation.
Mr Wahl said FIFA later apologized to him over the incident.
He also wrote this week that he had been among 82 journalists honoured by FIFA and the international sports press association AIPS for attending eight or more World Cups.
A 1996 graduate of Princeton, Wahl worked for Sports Illustrated from 1996 to 2021, known primarily for his coverage of soccer and college basketball.
