Real Betis have warned Premier League clubs over Benat's asking price.
"Benat's clause is 20million and he will only leave for 20million," Mel said.
"To sell him for anything less would be a disaster. The club must defend its position and Benat knows that. To be able to go the market and find a replacement, the only number is 20million.
"He has one more year left on his contract and he can fulfill that."