On paper, Osasuna's match against Real Madrid on Saturday has only one outcome: the team propping up Primera against the reigning champion.
But several times this season, the form sheet has been torn to shreds in much the same way as Real's defense has been. And traditionally, Real doesn't much enjoy its away days at the former Reyno de Navarre stadium (now reverting back to its original name of El Sadar after the regional government withdrew it sponsorship. Cutbacks, and not in the footballing sense.).
Without delving too much into politics, Navarre is one of the areas claimed by nationalists as an integral part of Euskal Herria, the swathe of territory in northern Spain and the south of France that constitutes the historical extent of Euskadi, the Basque homeland.
It's enough to ensure that Real never receives anything near a warm welcome in north, where sub-zero temperatures are not uncommon at this time of year.
Cristiano Ronaldo recently said he feels loved as much by the Bernabeu as by fans in Spain's scattered stadiums. Forget that in Pamplona. Football cliche often refers to the 12th man. Osasuna will have a whole bench in the stands when Real comes to town. Even more so with the cloak of invincibility rudely ripped from Real's back this season.
Two seasons ago Osasuna ambushed Real for a 1-0 home win. So far this season, Jose Luis Mendilibar's team has rarely been beaten by more than a single goal, and has dished out a couple of high-scoring losses against Levante and Espanyol.
The home side's conundrum is that while it is mean in defense, it is toothless in attack. Although bottom of the pile, Osasuna has conceded the same number of goals as Real and just one more than runaway leader Barcelona. Unfortunately, it is also the division's joint-lowest scorer, alongside Granada, with 14 strikes.
This isn't going to be one for the purists, but Osasuna's fans won't care as long as it stays reasonable. And they have a new chance to jeer Ronaldo's every touch of the ball.
Here are five key areas where the difference will be decided between the teams.
A few days ago, this match would have been overshadowed by goalkeeping concerns for both sides.
In the case of Real, had Antonio Adan started again, even the stanchest Madridista would be forced to the conclusion that Jose Mourinho is trying his best to get sacked.
A red card in Adan's last outing saw Iker Casillas brought into the fray, and tellingly offered the captain's armband by Ronaldo. Casillas refused it. Any notion of holier than thou is quite misplaced in the case of the Real captain. He simply wishes to play, and to win.
It is safe to assume Osasuna would have preferred Adan between the sticks. Especially after a medium term injury to Asier Riesgo forced Mendilibar to coax 41-year-old Ricardo from his pipe and slippers and back into his gloves.
The veteran stopper, who retired last season, said at the time he thought it was a joke.
Mendilibar apparently thought handing former Mallorca B keeper Andres Fernandez the job would be far less amusing.
Expect Ronaldo to test the old man's rusty joints as early as possible if Ricardo gets the nod.
The Reyno de Navarra
Another football cliche concerns cold (add weekday) away games at (add grim industrial town) with the crowd and weather conspiring against you.
I have a personal fascination in seeing how Leo Messi would fare against, say, Hull in a League Cup tie in a good old-fashioned English David-against-Goliath tie.
Bradford City have been doing a decent job of proving this point so far this season in the same competition.
Of course, Messi will probably never wind up at Villa any more than David Villa will wind up at Arsenal this winter. To witness something similar in La Liga, dump Ronaldo in the Reyno.
Osasuna is about as close to an English bruiser as you get in La Liga. Although I doubt Stoke will get into the Champions League in a hurry.
The crowd will be firmly behind Osasuna and equally ready to howl with glee at each scuffed touch from the world's most expensive player on another frozen pitch, as was the case at Valladolid.
Ronaldo scored his first goal in the Reyno de Navarra in the same fixture last season. Then he added his second. And assisted two others in a 1-5 demolition of the home side. That will not make it any easier to repeat the trick, especially when the chant of "Messi, Messi!" inevitably fills the frigid air.
Kike Sola, alone against the world
To say Osasuna lacks a creative outlet in the final third is like saying Messi is a bit handy. Most of this role falls on Kike Sola, and to a lesser extent Roland Lamah and Emiliano Armenteros.
The latter two constitute the foreign "spark" in a squad mostly containing Spanish journeymen. The trio has managed eight goals and six assists collectively in 18 games.
This is going to be a game largely decided at the back. Or by a lot of crosses aimed at the head at Joseba Llorente, if the Basque striker gets a game.
One goal this season suggests he won't.
Osasuna's back four
Osasuna is essentially a Primera Division club because it can defend. It's something of a tradition. With little in the way of attacking flair as a general rule, the academy produces notable defenders such as Javi Martinez, Nacho Monreal, Cesar Azpilicueta and Andoni Goikoetxea, then buys in striking has-beens like Savo Milosevic and Walter Pandiani.
In its current guise Osasuna, has a bad-ass back four led by veteran center-half pairing Miguel Flaño and Alejandro Arribas, with Patxi Puñal, whose name roughly means "fist" in Spanish, patrolling the defensive midfield area.
Mendilibar isn't likely to risk much going forward. It's going to be a rough ride for Real's forwards.
The ups and downs of the cup
The cup giveth, and the cup taketh away.
Osasuna crashed out of the only domestic competition any side other than Real or Barcelona can aspire to against Valencia's reserves on Tuesday. A full-strength Real saw off resolute Celta a day later.
Part-timer Luka Modric excelled against the Galicians, and Ronaldo expelled any lingering Ballon d'Or rancor with a hat-trick.
Had results gone the other way, Osasuna might have been riding a wave and Real staring down the barrel of a double wipe-out domestically. But Mourinho's team moves into a quarterfinal against Valencia with the carrot of a semifinal against Barcelona beckoning.
Osasuna has only the misery of a relegation battle to look forward to now. Real will be on the receiving end of the backlash, but it's unlikely it will make much difference to either's league standing by Sunday.
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