The Brazilian would fit into several different systems but would leave the team vulnerable at the back. If he does join, Zidane's tactical set-up would be key.
If Neymar does end up joining Real Madrid, Zidane would have to completely rethink his system to accommodate the Brazilian. Apart from finding a place for Neymar in the team's attack, tactically, there would be other problems to resolve.
The pre-season also showed Madrid have not rectified their deficiencies in defense; 16 goals conceded and 105 shots against in six games suggests that not only is the team just as vulnerable at the back as it was last season, but it is also arguably worse. So Zidane would need to find a place for Neymar in the team without weakening the left channel.
Neymar in a classic 4-4-2 or rhombus formation
The simplest way of fitting Neymar into the team would be playing him as a winger or left-sided forward. How he is able to link up with Hazard will be key in how the rest of Madrid's attack would take shape. The left wing is Hazard's, but he can also play more centrally just behind the centre-forward or even swap roles with Neymar but that's more complicated than it sounds.
In a 4-1-2-1-2 rhombus system, Neymar would play just behind strike pair Hazard and Benzema. The midfield would be comprised of two players covering the wings (Modric and Kroos) and one holding midfielder (Casemiro).
Another variation would be the classic 4-4-2 with Hazard out wide on the left and Kroos and Casemiro forming the midfield pivot. Hazard and Neymar could interchange roles as long as the left flank is covered when Madrid aren't in possession. Neymar performed this role many times in Barcelona. The only snag is who would occupy the right-wing.
It's unlikely that Zidane will opt for a 4-4-2, a system which has gone out of fashion in recent years; it could also unbalance the team on and off the pitch as it would mean sacrificing Vinicius for a midfielder and all the risks and potential consequences that might go with that.
Modric could move into a central position when the team is attacking and switch to the wing when they lose the ball. A 4-2-3-1 would involve organizing the attack in a similar way.
4-3-3 with Ney on the wing
While Zidane stated towards the end of last season that he would be reviewing and changing his system, he hasn't strayed from his traditional 4-3-3 during the pre-season.
It would be a huge surprise to see Neymar playing out on the right, that would also leave Lucas Vázquez and Bale out in the cold.
A 4-3-3 would allow Hazard, Benzema and Neymar to play together as a dynamic, three-pronged attack - with Neymar out on the left, and Hazard and Benzema interchanging positions when the team moves forward.
Pairing up with Benzema in a 3-4-1-2
There is an option for Zidane playing a 1-3-5-2 - with Neymar accompanying Hazard as the front two and Isco playing just behind them - effectively changing the 1-3-5-2 to a 1-3-4-1-2. Neymar could link up with Marcelo on the left channel with Hazard given freedom to look for spaces behind enemy lines. The only setback with that would once again be how the team copes defending.
But that system hasn't worked well for Madrid - when attacked, the team is frequently left out of position with Casemiro and three center-backs left to do all the clean-up work.
There are roles which Neymar could fill at Madrid but that would involve all of the front three dropping back to help out with defending duties or pressing in the final third. In the end, it will be Zidane would decide whether he needs Neymar or not but the feeling is he would rather sort out a midfield which has been giving him all kinds of problems since last season.