McFadzean, 29, has been linked with a move to boyhood club Sheffield United after making 44 appearances last term.
"If Kyle wants to go, £500,000 is the asking price for the best centre-half in the league," said Robinson.
"I don't care about what he thinks. His agent's been excellent, but we've not spoken to Kyle."
McFadzean was a trainee with the Blades, before joining MK in 2014 after spells at Alfreton and Crawley.
He helped the Dons win promotion to the Championship in his first season at Stadium:MK, but they were relegated back to League One last term.
Meanwhile, striker Nicky Maynard has signed a new one-year deal with the club - but Robinson has been frustrated so far in his attempt to add a winger to his squad.
"[Nicky] was the one I wanted. I didn't hide my desire to sign him," Robinson told BBC Three Counties Radio.
"One wide player wanted to sign here, but something else came up that we were disappointed by.
"We met a Premier League club last week about one of their players and I'm meeting one on Tuesday to speak about some of their loan players on how we can aid the development of their players, which equally aids and supports the development of the football club."
MK Dons manager Karl Robinson insists he has not spoken to Kyle McFadzean, following reports the defender has handed in a transfer request.