United beat QPR 2-0 in London yesterday.
"The players' contracts is where the [real spending] issue lies [for struggling clubs]," said Ferguson, for whom Phil Jones is a major doubt today. "Some will be on very good contracts in the Premier League and dropping into the Championship, how the motivation starts is very difficult I would imagine. Clubs have to pay their contracts. The only place you want to be is the Premier League and that's reflected in QPR spending the money they have done and other clubs also."