Well, it's Rafters role to get DC wins. He's not going to like players tanking and not giving 100% and he is going to want players who are doing well to play for the team. Tomic is erratic enough to fit both categories over the course of a few months.
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM