Unhappy player

[McLovin]

I'm new to this game so I've taken on Chelsea. I'm in the preseason transfer stage and my DC Carvalho is unhappy and wants to leave. I kind of need him, should I keep him even though he is unhappy or should I list him. If he stays will he play crappy?

[Big Fo]

Give it a few months, if he's still unhappy sell him in the January transfer window (assuming he has a multiyear contract at the present). If he's playing regularly and your team is winning games he'll likely get over whatever is bothering him.