A late goal from substitute Juan Albin gave Espanyol a share of the points and Barcelona are now 13 points clear of them in La Liga after beating second-placed Atletico Madrid 4-1 thanks to yet another double from Lionel Messi.
"The league is now impossible," said Mourinho. "It is the first time that I have been in a situation like this where my team are a long way off their objectives.
"But I don't want to make a drama out of it, I will treat it as another stage of my life.
"It is practically impossible. There are too many points to make up at this stage. Last season, we had a 10-point lead in February and La Liga was ours.
"Cristiano (Ronaldo) played well but his team-mates didn't. The attitude has been good and what we need is a bit of calm and luck. For the effort of the players we deserved to win but we wasted clear cut chances."