The former England international scored 141 goals in 238 games for hometown club Boro between 1954 and 1964 and won six caps for his country.
Peacock, 83 - whose prodigious aerial ability was rated alongside that of John Charles, Nat Lofthouse and Tommy Taylor - moved to Leeds for a then club record £55,000 in February, 1964 and scored on his United debut at Norwich City and on his return to Ayresome Park with his new club.
He fired doubles in the spring victories at Swansea and Charlton Athletic, which clinched promotion and the Division Two championship respectively at the end of the 1963-64 campaign under Middlesbrough-born Don Revie.
But a serious injury to his right knee during United’s tour of the former East Germany that summer ultimately proved the beginning of the end for Peacock, who had to wait until February, 1965 to feature in the top-flight with United, going onto pick up a losing final medal after the 2-1 loss to Liverpool in the FA Cup final that May.
A return of nine goals in 16 games at the start of the 1965-66 campaign - accompanied by an international recall and his third goal in six games for his country - hinted at a lasting renaissance.
But he later suffered more ligament damage to his right knee in the second half of the season to end his 1966 World Cup dreams - Geoff Hurst famously going onto spearhead England’s successful tilt at glory - and all but finish his United career.
He later joined Plymouth with his career ending at the age of 30.
In a statement issued on Boro's website, Peacock, 83, a familiar face around the Riverside on matchdays where he is a popular hospitality lounge host and tour guide, said: “It saddens me to hear and read about many of my old teammates and opponents now suffering from dementia.
“I was diagnosed in 2018 with Vascular Dementia/Alzheimer's disease. At the time, it didn't really sink in, but as time has gone on I realise I'm not quite the man I was a few years ago.
“Although my career was sadly and devastatingly cut short due to injury, I actually feel lucky. Perhaps if I had carried on playing, I might have been affected at a much younger age.
“Much has been debated about the weight of the old footballs, especially when wet, possibly contributing to the number of players now presenting with the disease. I'm not sure about that, but it really was like heading a cannonball at times!
"Having said that, I wouldn't change a thing. I love the game and am extremely proud to have been fortunate enough to play for my hometown, the mighty Leeds United and of course, my country.
“I am, and intend to stay, positive. I enjoy going to the Riverside, being involved with the club, watching home games and catching up with everyone. I really missed it during lockdown.
“There are naturally good days and bad. The good days far outweigh the bad at the moment and I'm hoping it stays that way for a long time to come.
“I am aware that there is ongoing speculation about my condition which fortunately has been progressing slowly.
“My family and I are hoping that, by publicly acknowledging my illness, it will raise awareness and encourage further research and support for everyone affected by this terrible, progressive disease.
“In the meantime, Up The Boro!”