Having a hard time winning despite having some star names in the squad? Then have a look at how well they play as a team.
Players can only improve their Teamwork skills by playing more matches.
No matter how good the player is, it's meaningless if due to poor Teamwork no one picks up his movements or passes to him.
Be patient and give him the time he needs to fit into the side.
If that's not enough, may be it's time to overhaul your coaching staff