Ferguson has praised Andre Villas-Boas' management of the striker.
He said: "They are going to be a challenge for that top-four position. The lad Defoe has had an incredible season. There's been goals for him.
"They signed Emmanuel Adebayor from City and he never played him. He kept playing Defoe all the time and I think it's given the boy confidence. So he has done very well. Adebayor's away to the African Nations Cup so they don't have him but they have Dempsey. It's a strong squad.
"Down there, there seems to be a lot of goals in the games. White Hart Lane's a good ground for us and Spurs are always going to have a go at you."