Rotation feasibility
We have spoken about this but we will emphasize again. Madrid cannot rotate before the possible semi-final as it is against Alaves who are tailing them in the league, they cannot rotate in the Clasico or in the Madrid Derby and UCL tie.
Tough times. Even if they try against Alaves, Varane is out suspended, which is bad already. Maybe in midfield. But these problems are occurring because Solari ceases to start Isco.
Barcelona can afford rotations against Athletic Club, surely in the defence and maybe midfield. Their concern will be Jordi Alba. One more yellow card will put him out of the league game.
The only backup left back is Miranda. But that is about it. Take Busquets out, you still have Rakitic, Arthur and Vidal. Even a 4-4-2 is feasible with Coutinho and Sergi as wide midfielders. Even before UCL, they have a Valladolid game to rotate.
Final opinion
An El Clasico, not one but two, seems really lucrative on paper. Both fans would be willing to see the game but there might be some who opt out of it, including me. Barcelona has to rotate in the game against Valladolid but this team defended till death in the first game.
Athletic Bilbao held Barcelona scoreless till 83 minutes or so. Attacking rotations are risky here, so if they find an easy Copa Del Rey opponent, the issue is solved. Rotate there, start the good ones here.
Madrid might not be serious about the league as it is almost out of reach. But the Madrid derby, El Clasico, and UCL Round of 16, all will arrive in just under a week.
It is too bad for a team recovering from a bad phase to undergo these challenges in a quick span of time. A loss will further deteriorate their confidence and take a toll in their UCL bid.
Barca vs Madrid, Last meeting: Barca won 5-1 at Camp Nou and 3-0 at Bernabeu
The last meeting in CDR: Final 2013/14, Madrid won 2-1
So this is my opinion and mine only. What is yours? Just drop down in the comments.