It seems that Xavi will use De Jong as replacement for Lewandowski if he cannot recover and play in the match against Real Madrid but De Jong is also playing after recovering from his injury so Xavi has to really consider everything so that nothing bad happens to his players.
However on the other hand some of the latest news also states that Lewandowski can recover on time and can even take part in El Clasico and this is good news even though it is not necessarily true.
But despite all the rumors that have been circulating it seems that Xavi knows more about the Barcelona squad so he can have better plan to be able to perform optimally in El Clasico.
Lewandowski is one of many important Barcelona players currently sidelined due to injury. Lewandowski's injury is making Xavi worried. This is no different than a shock for coach Xavi. Lewandowski is Barca's number 1 striker this season. But what's worse is that right now, Coach Xavi doesn't have a valid "number 9" to fill Lewandowski's void. Lewandowski will not take risks in El Clasico if he is not physically fit. De Jong replacing him is also an option. However, in terms of effectiveness, you should choose Ferran. Don't forget that Ferran is no stranger to the role of "false number 9".