But Moorcroft reckons two more gold medals over 5,000m and 10,000m in Glasgow would crown an achievement that would never be repeated.
Farah, the double world and Olympic champion, has seen his build-up to the Games hampered by illness and a lack of races.
The 31-year-old was admitted to hospital with abdominal pains, forcing him to miss the Sainsbury's Glasgow Grand Prix at Hampden Park and, while he returned to full training last week, he also pulled out of last Sunday's Anniversary Games, opting to remain at his altitude training base in Font Romeu.
His only track appearance this year came over 5,000m at the Portland Track Festival in June, while his two other races - the New York City Half Marathon in March and the London Marathon the following month - hardly went to plan.
He collapsed after crossing the finish line in New York and could only manage a disappointing eighth place on his marathon debut in London.
Moorcroft, the 1978 Commonwealth 1500m champion, said: "I think it could be his two toughest races for many years (in Glasgow), but he's already a legend, that can never be taken away.
"If he was able to do the double at the Commonwealth Games, which is really hard because of the Kenyans and other Africans, in the four years between 2010 and 2014 he'll have done something that no other athlete's ever done and probably no other athlete will ever do in the future - that is to be double gold medallist at Commonwealth, European, world and Olympic (level).
"That is staggering, almost unbelievable and to do that within a four-year period when he's gone from being a really talented athlete to dominating the world is truly astonishing."
His hampered preparation might leave the door open for his Kenyan rivals, but Farah is a master at triumphing against the odds. And, over the last couple of years, he has always had the measure of the opposition when it matters.
"I think if he's in decent condition then he'll find a way of winning," said Moorcroft, the director of sport at Join In, a London 2012 legacy initiative designed to get more people volunteering in community sport.
"If they've got any sense they'll smell a weakness. They'll know, if Mo's beatable, then Glasgow is when he can be beaten.
"You could say they've got an opportunity now because Mo's had this problem, but, having said that, they'll be looking across and thinking, 'Oh s**t he's there'.
"If, as the race unfolds, he looks strong and he looks positive, then gradually they'll be more and more worried about Mo."
Farah has five global and three European outdoor titles, but has yet to win a Commonwealth medal.
The 5,000m is a straight final in Glasgow - at previous championships Farah has had to come through a heat - and will take place on Sunday evening, the opening day of the athletics programme. He then has five days to recover for the 10,000m final.
Moorcroft, who lost his British 5,000m record to Farah, added: "He doesn't need to prove anything to anybody other than himself now. Every gold medal he wins now is a massive bonus.
"The Commonwealths has just got this extra dimension, potentially he could do that incredible quadruple double."
:: David Moorcroft is director of sport for Join In, a London 2012 legacy charity that puts more volunteers into community sport. For further information visit joininuk.org