The two clubs have agreed on a €2 million (£1.73m) fee, plus potential bonuses and a sell-on clause, with the player set to undergo a medical on Tuesday, according to Jose Maria del Nido.
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"We made him an offer and he didn't accept," Del Nido told his club's official website. "He wanted to go. We accepted that his agent might put him on the market and he has reached a deal with Crystal Palace for €2m, plus bonuses and a percentage of a future transfer.
"The logical thing is that he signs [Monday] and [on Tuesday] he travels to the United Kingdom to do the medical."
Del Nido claimed that he did everything in his power to make Campana a star with los Rojiblancos, and refused to accept any blame after the midfielder failed to become a regular starter in the south west of Spain despite having represented his country at youth level since the age of 16.
"I, when sat in the president's chair, try to be objective," he added. "When a canterano [club youth product] is made an offer to renew his contract and doesn't accept... and gets an offer from English football which is the best for the three parties, yes, we'll accept.
"Blaming the club or the coaches would be very easy. Campana was going to be a star but unfortunately he has not managed that. We have done everything possible that he would be a star.
"I told the coaches that there was a line-up of 10 players, that he had to play. I intervened so that Campana would play, understanding what these words meant. What more can we do? We hope that Campana does well at Crystal Palace because he's our product."