Diamanti for the right amount (max 7M) would be a wise investment imo.
An explosive player on the bench that can have an immediate impact on the match and offers tactical variation.
I think he's the player that will make the 3-5-1-1 work. Maybe when playing in the CL, our matches against Bayern Munchen have scared us a bit and we are planning to maybe use that formation against strong opposition in Europe?