I dont think we should sell Sissoko. He has been one of our absolutely best players, the last couple of years. When he played well, which he used to, I would say he was one of the best defensive midfielders. The whole team has underperformed this year, including Sissoko, but he has, as so many others, also been played out of position, in a retarded 3-man midfield, as a winger/high pressure player. Furthermore injuries has ruined his consistency as with the others.
I would be carefull to sell players like Sissoko, Marchisio, Melo, Poulsen, Diego and Amauri, as their value might have fallen, but their potential still remained.
Anyway, we still got a lot of players ready to ship for FC Cologne, with Grygera, Grosso, De Ceglie, Trezeguet, Zebina, Sali, Tiago and so on.