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."