"This club is experiencing a time of economic stability and we don't need to sell. We're going to be firm about this and we'll only consider selling outside the market, which gives us the opportunity to make our team competitive."
On Rakitic, he confirmed talks were ongoing over a new deal - despite the likes of Real Madrid, Barcelona and champions Atletico Madrid all reportedly readying offers for the Croatian.
But Castro did admit to being 'frustrated' with Rakitic over the fact he is yet to sign his deal.
"The contract renewal offer to Rakitic is really important to us, as a part of our budget for the next season. We want Rakitic to stay so that the team remains powerful, we really want him to stay," he continued.
"Rakitic still has a year left on his contract and we'll have to analyse what comes. The truth of the matter is that many months have gone by, since we reached an agreement with him and he's still not signed. We're frustrated about that and I am particularly."