The Citizens have made a storming start to the campaign, dropping just two points from the first 24 available to climb to the top of the division.
United are two points further back after making a solid start of their own in the first two months, but De Bruyne admits that neither side can afford any slip-ups if they are to remain afloat at the top.
Asked if the Manchester clubs will battle it out for first place, he told ESPN: "For the moment I think so, but everybody's still there. It's so early, if you lose two or three games you go back to a [lower] position. We have to maintain this hopefully."
City have the best goal difference of any side in Premier League history after eight matches, scoring 29 times and conceding just four.