Real Madrid's faint hopes of retaining their La Liga title receded further when they had Kaka sent off and were held to a 0-0 draw at struggling Osasuna on Saturday.
Jose Mourinho's side appeared lost without inspirational top scorer Cristiano Ronaldo, suspended for the game in Pamplona, and unbeaten leaders Barcelona can go 18 points clear of their arch rivals with a win at fourth-placed Malaga on Sunday.
Real stay third on 37 points, four behind Atletico Madrid, who meet Real Zaragoza at home on Sunday.
In a poor-quality and bad-tempered clash at Osasuna's Reyno de Navarra stadium, the main incident came in the 76th minute when Kaka was shown a second yellow card for preventing Osasuna taking a quick free kick.
The little-used Brazilian playmaker had been on the pitch for a little over a quarter of an hour and had been booked moments after coming off the bench for jumping with a flailing arm.
It was the 2007 World Player of the Year's first sending off since he joined Real from AC Milan in 2009 and his first red card since he was dismissed playing for Brazil against Ivory Coast at the 2010 World Cup.
Largely toothless in attack, Argentina forward Gonzalo Higuain had a frustrating game before being substituted, and even the introduction of Germany playmaker Mesut Ozil and France striker Karim Benzema in the second half failed to lift Real.
They dropped only 14 points in the whole of their triumphant 2011-12 campaign but have already drawn four and lost four this term, while Barca have won all their games except for a 2-2 draw at home to Real in October, when Ronaldo scored twice.
The Portuguese forward's absence was sorely felt, and Real have now failed to win the last three La Liga matches in which Ronaldo, who has scored 16 times this season, did not play.
Real defender Raul Albiol, handed a rare start at centre back in the absence of the injured Pepe and the suspended Sergio Ramos, suggested the club had given up on their bid for a second successive domestic title.
"The league has to help us for the (King's) Cup and the Champions League," the Spain international said in an interview with television broadcaster Canal Plus.
"To build rhythm and get on a run of victories that will allow us to perform well in those competitions," he added.
"We have to find a positive dynamic, although it's clear that things are not going well in the league.
"We should have won. This is a tough stadium to play at and we suffered with a man down, but there is no excuse."
Osasuna's well-earned point lifted them off the bottom of the table thanks to a superior goal difference compared with Deportivo La Coruna, who play at Real Sociedad on Sunday.