The two sides have also been evolving together over the course of the 2019-20 season. Real Madrid have been invigorated by the emergence of youngsters Fede Valverde and Rodrygo, with the Uruguayan midfielder, 21, and Brazilian forward, 18, both potentially match-winners as they head look to start El Clasico for the first time.
An issue for Zidane is on the left of the defence, where versatile utility-man Nacho Fernandez filled-in against Valencia on Sunday.
Tweaking the team
Barcelona have also been tweaking their side positively as the season has progressed, with summer arrivals Frenkie de Jong and Antoine Griezmann now more integrated into the Barça's trademark passing style of football.The return to prominence of Ivan Rakitic has also helped their midfield cohesion, while left-back Jordi Alba proving himself fit again on Saturday was another boost.
Much of the focus of Ernesto Valverde's men will again be on talisman Lionel Messi, who has 18 goals and nine assists in 29 career El Clasico matches in La Liga. Although Messi was missing with injury in the corresponding fixture last season, Barcelona still ran out resounding 5-1 winners at the Camp Nou, with Uruguayan star Luis Suarez stepping up with a hat-trick.
Zidane was, however, unbeaten at the Camp Nou in La Liga during his first term as Real Madrid coach, winning 2-1 in 2015-16 and securing draws during the two following campaigns.
Valverde also has an excellent record in El Clasico, with last March's 1-0 La Liga victory at the Santiago Bernabeu making it three wins and a draw in four meetings since taking the Barcelona job.
Tight to call
There is little to separate the two teams as they head into the next leg of world football's biggest club game, in front of a potential live TV audience of more than half a billion viewers in 182 countries.
The latest La Liga El Clasico really is too tight to call, so all we can do is tune in and wait for the excitement to begin. Audience in India can watch it live on Facebook Watch from 12.30am (Thursday, December 19).