Real Madrid were frustrated on the road in La Liga for the second time in a week in a goalless draw against Racing Santander at El Sardinero.
Jose Mourinho's side, who are attempting to end Barcelona's three-year stranglehold on the Spanish title, won their opening two games of the season but suffered a shock 1-0 defeat at Levante on Sunday.
They again looked short of ideas and creativity at Racing's Sardinero stadium and barely threatened the home goal in a generally lacklustre display.
Madrid mustered a single shot on target, with Angel Di Maria's 30-yard effort tipped over by Tono 10 minutes after the break.
And in the dying moments of the game the visitors were denied a penalty despite replays suggesting that Cristiano Ronaldo's free-kick was handballed in the area.
"This is two matches now without winning against opponents who to be honest do not compete with us," Casillas told Spanish television.
jose Mourinho's Real in particular need to buck up their ideas if they are to end Barca's three-year stranglehold on the title after dropping more points in an uninspiring 0-0 draw at Racing Santander in midweek following a shock 1-0 defeat at Levante on Sunday.
"We cannot ignore the evidence," Real's Spain midfielder Xabi Alonso said.
"The dynamic is not good and we have to change it as soon as possible," the former Liverpool player added.
"We have to pack more punch because matches like this (at Racing) take their toll and we cannot afford to drop many points."
Barca twice had to come from behind to rescue a point at Valencia, the early-season pace setters, who are top after four matches on 10 points.
Barcahave eight points, level with Sevilla and Levante, and Real Madrid are on seven along with Atletico and Real Sociedad.