Cagliari are demanding huge money for Radja Nainggolan.

The Belgium international is of interest to a number of sides this summer, but he won't be allowed to leave on the cheap.

"I've promised him that I would let him go if a big club came in for him with a bid," President Massimo Cellino told Unione Sarda.

"However, the offer has to be a big one - an offer that is not any smaller than €18m."