Spurs rebuffed a number of big-money offers from Chelsea for midfielder Luka Modric during the summer but Redknapp acknowledges the large part that money plays in the modern game.
"Players play for a club and they enjoy being there, but if someone comes along and offers them a contract that could blow their current one out of the water, then you've got a problem," Redknapp said.
"I'd be talking rubbish if I said people wanted to stay at Tottenham just because we're playing good football. I'd be dreaming. If you want to keep the best players, we have to find a way of doing a deal that's near to what they can earn elsewhere, otherwise it will be a problem.
"If you're a top player and someone wants to give you a fantastic contract, it's very hard to hang on to them."
Redknapp recently stated his desire to keep his current squad together in order to maintain his side's title challenge.