Gregg, 84, survived the 1958 Munich air crash which killed 23 people, including eight of his United team-mates.
"When the story broke I asked my wife if I could sit alone in the television room as I did not want anyone with me," said the Northern Irishman.
"I didn't know what way to react. It's very, very difficult to describe."
Speaking to his own charitable foundation's Facebook page, Gregg revealed that he had been contacted by a grieving Brazilian journalist following following Monday's tragedy in Colombia which killed 71 people including 19 players from the Chapecoense club on the way to play in the final of one of South America's major competitions.
"At Munich, I lost my friends and fellow players but there were others on board including one of the country's greatest journalists at the time," added Gregg.
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"When I told this Brazilian man this he said to me, 'Harry Gregg, I am so glad that you remembered everyone who died on the plane because I lost three friends on that aircraft who were sports journalists'.
"As with Munich the focus might be on the lost players but I told him we should never forget the others who died. I hope that gave this Brazilian journalist some comfort, as he was grieving too."
Gregg stayed with the burning plane in Munich after the air crash and helped to rescue a number of people, including a mother and baby.
Six people - including three players - survived Monday's crash close to the Colombian city of Medellin although goalkeeper Jackson Follmann's right leg has had to be amputated.
Gregg says getting back on to the training field following the accident "stopped me from going insane over what had happened to us all".
A few months after the Munich air disaster, Gregg was named the best goalkeeper in the world in honour of his performances for Northern Ireland at the 1958 World Cup in Sweden.
Ex-Manchester United keeper Harry Gregg says the plane crash which killed most of Brazilian club Chapecoense's players has brought back "painful memories".