Real Madrid will be without the services of star midfielder Luka Modrić through at least La Liga's winter break. Because Madrid play an ultra-attacking 4-4-2 formation without a real defensive midfielder, Modrić's versatility and work rate are as important to the team as Cristiano Ronaldo's ability to score and create goals consistently. If Los Merengues had a big match coming up, this would be concerning.
But Madrid don't have a big match coming up. They don't have anything that resembles a big match until January. Between now and winter break, the majority of their La Liga opponents are merely average, they already have a big lead in their Copa del Rey tie and they've qualified for the knockout stages of the Champions League. For their next seven matches, Real Madrid are either such favorites that Modrić's absence doesn't matter or are completely unaffected by a loss.
January's schedule is kind to Los Merengues, too. They face Valencia in the first game back from winter break, but then take on a slew of average opponents until February, when things get tough. Sevilla comes to the Bernabeu on Feb. 3, then Real Madrid take on cross-town rivals Atlético Madrid on Feb. 7. A Champions League match will follow shortly afterwards, so Madrid would certainly like to have Modrić back by then. But before February? No big deal.
Madridistas and Real Madrid-centric papers have debated Modrić's replacement since he went down. Will it be Sami Khedira? Asier Illaramendi? Or will Isco move into the deeper role that he occasionally occupied at Màlaga?
The answer should be "all of the above."
Finding the best possible replacement for Modrić probably isn't necessary for holding on to the top spot in La Liga, and it's certainly not necessary for advancing in Copa del Rey or getting a top seed for Champions League. Any of Isco, Illara or Khedira will do. Madrid could probably lose two of that trio plus Toni Kroos, plus one of Ronaldo and Gareth Bale, and still stay within one game of Barcelona in the league before Modrić comes back. They're the best team in the world at present and they're playing a schedule full of minnows.
All three of the players who could potentially replace Modrić should get a chance to do so. Multiple chances. And maybe youngster Álvaro Medrán should get a start, too. Carlo Ancelotti has absolutely nothing to lose by experimenting in Modrić's absence.
Of course, he might not see it that way. Ancelotti has a reputation as a pretty risk-averse manager, and might treat Celta Vigo and Màlaga as significant threats. Both of them did well against Barcelona, after all. But even if Ancelotti does pick the player he feels is best suited to help his team win immediately in those matches, he still has games against Cornellà, Eibar, Almeria and Ludogorets. The Basel match is irrelevant too, as long as Madrid doesn't lose by four goals.
Ancelotti has plenty to gain from this experience if he is willing to take some risks. Most importantly, more first-team football is good for any player, and it's likely that the players behind Modrić will get better (or, at least, not decline in performance) because of the opportunities they receive in his absence. Ancelotti can also gain some more information about his players, what roles in which they might be best utilized, and whether or not he can play any of these players at the same time as Modrić and Kroos if he needs to make a tactical shift.
Going into the spring, that will become increasingly important. Ancelotti can get away with fielding the same team, playing the same style, in the same formation and with the same defensive schemes in every single match this fall, but tactical minutiae and strategic surprises can make the difference in big Champions League, Copa del Rey and Clàsico matches at the end of the season. He might learn that he has more (or better) options as a result of the opportunities that new players get without Modrić available.
If he got injured at another time in the season, Modrić's absence could have been devastating for Real Madrid. In this particular instance, it might be a blessing in disguise.