Real Madrid's biggest problem is the lack of a central midfield player. Furthermore, I predict Arda Güler will be the player they'll use there, as his defensive skills are quite weak. He's also not as physical as Kroos, so using him in that position would be quite difficult. He could capitalize on his technical expertise to open up play, but Xabi would struggle defensively. In my opinion, Real Madrid needs a defensive midfielder.
It's true that Real Madrid midfield is a major problem, and we've seen that the flow of the ball from the back is often lost once it reaches the middle of the pitch. It's no wonder Xabi Alonso is still insistent on lobbying Madrid for support in recruiting more players. Xabi realizes that the current squad isn't enough to make Real Madrid strong.
Btw, Vinicius continues to be offered exorbitant prices by Arab clubs. Imagine his highest selling price in football history. If Real Madrid let him go, the proceeds would be enough to buy more players to fill Xabi's needs.