The league's bottom side visit the Bernabeu on Thursday having conceded 50 goals in 24 matches and arrive just when Real need to erase the memory of Saturday's goalless draw at Deportivo La Coruna.
That result enabled Barca to extend their advantage at the top to seven points on the weekend, and they could be 10 points clear by Thursday if they can overcome third-placed Valencia at Mestalla on Wednesday.
Real have won every home game so far this season but need a lift, in particular from their leading scorer Cristiano Ronaldo, who has netted only twice in the club's last nine matches in all competitions.
The Portuguese, their top scorer in La Liga with 24, is the only member of the team to have completed every single league match this season. "I don't see any reason to rest him," Mourinho has said. "If he needs to one day I will do, but he is very strong."
They will only have three days to prepare, compared to Real's five, after playing Almeria on Monday evening.
Barca's hosts Valencia have only lost once in their last 15 league matches, going down 2-0 at the Bernabeu back in early December, and have pulled four points clear in third. They remain 10 adrift of second-placed Real.
