Zinedine Zidane is expected to deploy his strongest Real Madrid side to take on Barcelona on Saturday [23 December] but the absence of Cristiano Ronaldo from training this week has sparked doubts over his participation.
The La Liga and Champions League winners have been plagued with injuries during opening part of the season.
Ronaldo has managed to stay healthy so far but he also missed the first domestic games of the campaign after being handed a five-game ban for pushing the referee during the Spanish Super Cup first-leg victory over Barcelona on 13 August.
Injury-prone winger Gareth Bale has meanwhile spent more than two months on the sidelines due to several muscular problems. Keylor Navas, Dani Carvajal, Raphael Varane, Marcelo, Karim Benzema, Luka Modric and Mateo Kovacic have also spent several weeks out of action due to different fitness issues. Even captain Sergio Ramos recently had to miss a few games after breaking his nose during the derby against Atletico Madrid.
Some may argue that those setbacks have contributed to an inconsistent start to the season which have seen Los Blancos accumulate just 31 points in 15 games, 11 fewer than Barcelona, although they still have a game in hand.
Ronaldo has not trained with his Real available teammates this week but, knowing his competitive instinct, it seems difficult to envisage the Portugal international missing such a massive game unless he is suffering from a serious injury.
Furthermore, the visit of Barcelona will arrive just before the Christmas break, a period which will allow Ronaldo to put his fitness woes behind him and prepare properly for the second half of the campaign.
So if there is a game in which Zidane could risk the fitness of the five-time Ballon d'Or winner then El Clasico seems like the perfect time to do it.
Same XI that for the Champions League final
Zidane could use the same starting XI that helped Real to win the Fifa Club World Cup with a 1-0 victory over Gremio in the final played on Saturday [16 December] at the Zayed Sports City Stadium in Abu Dhabi.
Indeed, it was the same line-up that months before also beat Juventus in the Champions League final to lead Los Blancos to the European trophy for a record 12th time.
Carvajal, Sergio Ramos, Raphael Varane and Marcelo should form the back-line of four with Nacho ready to step up in case one of the regular starters suffers an unexpected last minute injury.
Casemiro will be key to stopping Barcelona's passing game while Modric and Toni Kroos face a major challenge in a match in which both teams are expected to try to dominate possession.
Bale as super-sub
Karim Benzema remains immovable in attack with Ronaldo while Isco has emerged as the favorite to fill the final attacking position.
The situation is similar to the Champions League final when Bale started on the bench following a long-term spell on the sidelines.
Bale played some minutes in the semi-final and the final of the recent Club World Cup but Zidane will surely want to avoid risking the Welshman given his recurrent fitness record.
He scored the winner during the 2-1 victory over Al Jazira Club in the last four after coming off the bench and he is expected to have the same role again against Barcelona.
Asensio instead of Isco?
The introduction of Marco Asensio in the starting line-up ahead of Isco could be Zidane's secret weapon to provide more speed in his attack. The Spanish starlet was one of the best Real performers in the last two El Clasicos played at the beginning of the season in the Super Cup, scoring a goal in each leg to help Los Blancos draw first blood.
Yet, the most likely scenario is the former Mallorca winger to wait for his chance from the bench and come on alongside Bale in the second half in the event Zidane's side need late inspiration.