"There is a borderline in terms of what you would think is a good signing for United," he said.
"I see some values on players, like Hazard for instance. To me it was a lot of money. He's a good player, but £34m?
"What we're finding anyway, the climate for buying these top players - not just the transfer fees, the salaries, agents' fees - is just getting ridiculous now."
The United chief added: "In the Hazard deal, Chelsea paid the agent £6m. The (Samir) Nasri situation was the same.
"It's all about what you think is value for a player. I am not envious of those deals at all. We placed a value on Hazard which was well below what they were talking about. So if it doesn't work, well we're not worried about that."