I just think Demi will be off by January and in regards to Denayer, as good as he he is I really would be surprised if City are willing to put absolute faith in him and be reliable for 20-25 games this season.
If Demi goes we need an experienced defender to replace him and with Otamendi being arguably the best defender in La Liga last season I can see why Txiki is interested.
I still think central defence needs to be looked at.
Demi is likely to leave soon, Vinny is injury prone, Mangala is hot and cold and Denayer is still very inexperienced.