It has emerged that Bacuna cost around £800,000 from Groningen after previous indications suggested he arrived for more.
"Yes, Leo was a bargain but Westwood was probably cheaper," said Lambert. "Matt Lowton was around the same mark. Luna was the same - around that mark.
"When you look at it, I see figures that are bandied about with some of my players
"I think somebody must be getting a backhander because they're nowhere near that level of money!
"So I don't know where the figures come from. It makes me laugh because it's nowhere near that."
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