The Catalans could have drawn within four points of the leaders with a victory at the Reyno de Navarra but, as their coach admitted, the defending champions now look set to fall 10 points back, with Los Blancos expected to see off Levante at the Santiago Bernabeu on Sunday evening.
"The reality is that we are at a substantial distance behind Madrid and I get the feeling that gap will increase tomorrow [Sunday]," Guardiola told reporters after the game.
"But we have to keep on going until the end. We don’t really have many perspectives to work from: we can only play the next game as best we can."
Guardiola all but admitted, though, that the club will now focus on the retention of their Champions League crown, heaping even more importance on Tuesday night's last-16 first-leg clash with Bayer Leverkusen.
"Now we will try to defend the title of European champions," he declared. "We have to defend our position in the Champions League and then we'll play the next match against Valencia [in La Liga] at our best."
There was controversy in Pamplona, with Alexis Sanchez seeing what would have been a late equaliser ruled out for offside, while the frozen pitch was hardly conducive to free-flowing football.
However, Guardiola was not looking for any excuses after only Barca's second defeat of the season in all competitions.
“If we were playing well in the second half on this pitch, we could have done the same in the first," the former B team coach reasoned.
"Osasuna started off well and adapted to the pitch and the cold better than we did. We struggled to get into the game.
"At the start of the match we could not win a ball, but in the second Sergi Roberto and Thiago battled well in the midfield. [Cristian] Tello and [Isaac] Cuenca were also very good and opened up the field.
"Anything could have happened in the second half, but congratulations to Osasuna."
After their midweek trip to Germany, Barcelona will be out to try to reduce the gap between themselves and Madrid when they face Valencia at Camp Nou on Saturday.
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