The Lilywhites brought in four new players during the latter stages of the summer for a combined £86m, balanced out by the departure of Kyle Walker to the Citizens for £53m earlier in the window.
City set a transfer record when splashing out big to overhaul the defensive aspect of their squad, meanwhile, and United also brought in the likes of Romelu Lukaku and Nemanja Matic for large sums.
Pochettino admits that it is tough trying to live with the Manchester clubs in particular, telling beIN Sports: "The difference these days between clubs in the Premier League is that there are clubs, like City and United, who sign who they want and when they want.
"Then there are big teams, like us, who sign when we can and who we can. It's the big difference today."
Spurs trail United and City by five points in the Premier League table with seven games played.