With Barca and Atleti playing each other on Saturday, Carlo Ancelotti's side will make ground on one or both of them if they can extend their unbeaten run over Espanyol to 12 games.
Espanyol have endured an inconsistent season under Javier Aguirre so far with only six league wins to their name, although one of those did come against Atletico at Estadi Cornella El Prat in October.
The Mexican may not be on the sidelines though after being sent to the stands during last week's 1-0 defeat to Osasuna, if he is found guilty of abusing the referee he could face a touchline ban starting this weekend.
Stopping Real Madrid will be difficult given the 32-time league winners have amassed 31 goals in their last eight league matches, with forward Cristiano Ronaldo getting 12 of those to take him to the top of the goalscoring charts in Spain with 20 for the campaign.
The Portugal international is one of the most in-form players across the continent and is odds-on favourite to lift the FIFA Ballon D'Or on Monday after his displays in 2013.
Real are unbeaten in eight games in the league and Ancelotti is demanding a win from his players when they travel to Catalunya, although he is unsure which result he would like to see emerge from the Estadio Vicente Calderon.
"It is hard to think about what the best result (between Atletico and Barca) for us would be," the Italian said ahead of the match.
"They cannot both lose, but neither can they both win. We have to win to make up points with Barcelona or Atletico."
Espanyol have earned draws in their last two meetings with Real, however they come into the game on the back of consecutive defeats in the league and Wednesday's first-leg Copa del Rey tie with second -tier Alcorcon.
Raphael Varane and Sami Khedira (both knee) are the only players unavailable for the visitors but Aguirre will be without his captain Sergio Garcia through suspension and David Lopez after he picked up a thigh injury in midweek.
