The manner of the negotiations angered Del Nido.
He told his club's website: "We were treated badly and that's putting it mildly.
"The fee was 7.5million euros plus add-ons, payable in several instalments. They demanded payment up front at the last moment.
"That was just one of many 'adventures' in this affair. One problem followed another. Fortunately, the player really pushed to arrange things.
"It's the worst transfer (negotiation) I've had to work on in my career."