Its interesting how people on this forum are split on this one. And its understandable.
Gana is one I'd put in our team this season most of the time. But, its only because we're seriously lacking in that department.
To be honest he's also a bit frustrating because in some matches he's been good (very good). Breaking play up, chasing players down etc etc. And, in other games he's been very average or poor. Giving the ball away, passing back to the centre backs too much etc etc.
I'm not adverse to him leaving (and good luck to him...its PSG after all). The key is getting a good fee and a suitable replacement (even if its in the summer).
Yes, it'll maybe be detrimental in the short term (rest of the season). But, just get through this season. Then longer term, in my view, we need to re-think on our personnel in centre midfield.