Ferland Mendy's signing will have a immediate impact with the organization of the team, he is not a straight up replacement for Marcelo but he comes with his own unique skillset which will be of help to us in the near future.
To give you an idea about Ferland Mendy - he is a two footed player, he is press resistant and quite good in 1v1 situations. He is a player who fits Zidane's style and I believe he'll be a integral part of the new core which we are building. Although he is a decent crosser, Ferland is pretty creative when it comes to passing, he goes for the risky passes rather than easy ones (something we need in this team).
He also offers the element of surprise as he at times cuts in and shoots with his right (being 2 footed comes with its own perks).
Madrid have paid 48M for Mendy, which makes him the most costliest fullback which we have bought, this also increases our expectations as fans on him but we will have to show patience as he'll require time to settle in. We will get to see a glimpse of his abilities soon enough once the pre season begins.