Although i actually like Costa and wasnt against the idea of signing him its a moot point regarding his workrate, particularly if he is to play that left side and bench Mandzukic?
He did better when he was given regular starts. You can't really expect a player like this to start 14 games and have a strong season, they need consistency. It's like Cuadrado with Chelsea or when he played as a sub for us, you get mostly shit from these type of players.