He shouldn't be asking for anything close to world class wages, and if he is, let him go., or tell him no, and see how he responds.
I wouldn't mind the player staying, but he shouldn't be a starter. I also think he could become a really good player, but he should be on, and remain on, substitute wages as he has done nothing to justify more.
More power to any club willing to pay him a superstar's wage, and fairplay to his agent if he finds one. There's no way Barcelona are that club - if he went there, he'd be a squaddie, at best, but I highly doubt they have any interest in him as he does not have the skill/technical profile they look for in forwards.