Barca are ten points clear of Real after victory last night over Atletico Madrid.
Asked if his side should forget about the league, Mourinho said: "What we need to do is forget about the Copa del Rey until the final, which is at the end of April.
"Now we need to think about the league and the Champions League, in which we have the same chance of winning it as the other 15 teams that are still in it.
"In the league we are behind and for this reason the favourites are those in front. Mathematically it's possible, and what's mathematically possible, is possible.
"We need to continue winning games and doing our jobs."