"He was quite funny. He said the young lads he'd got there were the ugliest bunch he'd ever had; said he could do with signing someone like me."
But despite his good looks, Jackson's dream move never materialised and when Manchester City also said no, the youngster returned to Rushden and Diamonds, where the beginnings of a career began to take root.
And now that short career – hitherto very modest – is given a chance to gain some momentum. On Sunday, in front of a nationwide television audience, not to mention a packed Priestfield Stadium, Gillingham's top scorer flirts with the big time once more when Aston Villa come calling in the FA Cup.
It remains to be seen whether this third-round tie turns out any better for Jackson than that earlier stay in Manchester. What can be said with some certainty, however, is that, to get to this point, his journey has proved more testing than most.
At the age of three he was packed off to Canada, separated from his parents in Jamaica. "My auntie and uncle lived in Canada," he explained yesterday. "And there were better opportunities over there, especially with schooling."
Jackson settled down to life in Ontario, while developing an obvious talent and love for football. So much so that, by the age of 15, and attracting several inquiries from this side of the pond, he felt brave enough to leave home in pursuit of his dream. "I always wanted to play football professionally," Jackson says. "I had my British passport so it was a good opportunity to come here and give it a go.
"I went to live with my great aunt in Croydon. It was difficult. I was starting afresh. New school, new mates, new everything. I just had to get used to it. It was tough, a real culture shock, but I knew what I wanted out of it so I was prepared to do it."
All well and good, but only a few months down the line, having joined Gillingham on schoolboy forms, he got released by the Kent club.
"Looking back, that was tough. I'd only just come over to England and all of a sudden I was being rejected. I thought, 'What do I do now?' " The not-so-glamorous answer was to join non-League Dulwich Hamlet, after failing to impress in trials at Bolton and Blackburn.
At that point, I wondered, did he not think his decision to leave Canada had turned into a horrible mistake?
"No. You just have to stay focused during those times and remember what you want out of it. It's easy to get downhearted and think you're never going to get anywhere. But I just kept on playing because I knew people were always watching."
They were indeed. And in Jackson's case, that person turned out to be Brian Talbot, manager of Rushden, who offered the striker a crack at the Football League.
"We got relegated to the Conference but that was a good education," Jackson recalls. "You'd get beat up every week but it taught you to look after yourself."
The forward did just that, recording very impressive scoring figures once he had got over the disappointment of United's rejection. What does he take from that fortnight? "I just remember the quality up there, training alongside players like Kieran Richardson and Chris Eagles. It gave me a good idea of how good you've got to be."
Villa will no doubt remind him of that high standard, especially if the likes of Gabriel Agbonlahor and Ashley Young are selected to continue their exhilarating form.
Like them, Jackson has great pace, an asset that has helped him reap 11 goals this season, having rejoined Gillingham a year ago, as well as earn a call-up to Canada's senior squad. "I try to threaten in behind. That's a big part of my game. I'm not quick over 100 yards. It's more short, sharp stuff. And I love those little poacher's goals. I had one the other day that came off my head. Didn't know too much about it."
He would surely settle for a replica tomorrow. What's more, if it resulted in a Cup shock, the name of Simeon Jackson would inevitably receive a much wider airing, perhaps even leading to a step up in class.
There can be no doubt the lad is determined. How else to explain his story so far?
"I've always been strong-minded," he said. "I know where I want to go and what I want to do. When your mind's straight you can do anything you want."