Claudio Ranieri says if one of the Manchester clubs were in Leicester City's position, people would believe the title race to be "finished".
The Foxes, who host West Ham on Sunday, are seven points clear in the Premier League with five games remaining.
Ranieri says Leicester, having avoided the drop 12 months ago, make for a good story, but his side must win the title to be remembered in "30 or 40 years".
"We don't achieve anything yet," said the 64-year-old Italian.
"Football is very strange. If you weren't here in Leicester but somewhere else, maybe City or United, with seven points more, you would say 'it is finished'.
"At this moment you don't think this. Why? Because we are Leicester. We have to fight and we have to be focused and strong."
"I love the Champions League music"
Leicester have won their past five league games without conceding a goal and three more victories would assure Ranieri's side of the title.
A 2-0 win at Sunderland on Sunday secured Leicester a top-four finish and, barring a permutation that includes Manchester City and Liverpool both winning European trophies, at least a place in the Champions League qualifying play-offs.
Ranieri, who admits to being a fan of the Champions League anthem, now wants the Foxes to earn a group-stage spot.
"It is two matches and two matches is not the Champions League - I want to play six," he added.
"I don't think there is the music," he said. "I love the music.
"I think it will be a fantastic achievement. From the dream arrives the reality, but wait first."
PFA award for Ranieri's "sons"?
The individual form of Riyad Mahrez, N'Golo Kante and Jamie Vardy has seen them named on the six-man shortlist for the Professional Footballers' Association Players' Player of the Year award.
Vardy has scored 21 league goals and made six assists, while playmaker Mahrez has contributed 16 goals and 11 assists.
Meanwhile, Frenchman Kante has made more tackles (146) and interceptions (134) than any other player in the Premier League this season.
"I am very proud because they deserve it," said Ranieri.
"They are doing a fantastic performance in every match and I hope one of them can win.
"They are three sons for me. If one son wins I am very happy."
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