Louis van Gaal's side are red-hot favourites to progress to the fifth round, but former England striker Dublin – who left Cambridge to move to Old Trafford in 1992 – believes a surprise could be on the cards.
"I think Manchester United should win the tie with no problem, but if Cambridge give everything they've got and have 11 players playing out of their skin then there may be a surprise," he said ahead of Friday's match.
Dublin helped Cambridge – now in League Two – to back-to-back FA Cup quarter-finals during a prolific spell at the club in which he also scored the winning goal in the first Wembley play-off final.
His time at the Abbey provided a platform for a playing career that went on to span 20 years and included four international caps, and the 45-year-old remains grateful to the club that gave him his professional breakthrough after being released by Norwich City as a teenager.
"It was possibly the best learning curve I could have had in terms of leaning how you conduct yourself on and off the field, the amount of work that we did, the amount of miles that we ran," he added, referring to the strict training methods of his then manager John Beck.
"It was very old school. I went from a young boy not knowing my career, to a man able to stand on his own two feet.
"Getting my nose broken at least a couple of times off the ball taught me how to look after myself, too. I arrived as one person and left as another person."
Cambridge, who won promotion back to the Football League last season after a nine-year absence, held Manchester United to a 1-1 draw when the sides last met in a League Cup tie in October 1991.
Friday's visitors, who overcame third-tier Yeovil Town in the last round, are seeking to end an 11-year wait to lift the FA Cup.