Spurs are battling City for fourth place.
And Redknapp said: "We've done it for two years and I think you've got to keep doing it.
"It's tougher this year. Man City have just spent £160million or something, trying to finish above us. Look at the players they've brought in - Yaya Toure, David Silva, Alexander Kolarov - they've spent massive again.
"From their point of view, when you've spent that sort of money, if you don't get a top-four finish, well, it's not going to be good for them. They've got to be in, haven't they?
"They're definitely stronger. If we can finish in the top four again, it would be a bigger achievement than last year. It would be a fantastic achievement. And it's going to be harder next season."