As Souness said, if he can't score (or even look like scoring) when he has a midfield of Xavi, Iniesta, Xabi Alonso and sometimes Fabregas supplying him then he's going to struggle even more with the likes of Ramires, Essien, Mikel, Ramires trying to supply him.
I don't think its a case of him not trying though I think he's just lost all of his self-belief and confidence. Maybe he needs the off-season to fully recuperate and get fully fit ahead of next season.
Excellent couple of wins for Nited though and actually look to be playing a fair bit more football than we have done all seaon.