With Real Madrid embroiled in a battle for European survival, Osasuna and striker Ante Budimir are hoping to capitalise when the LaLiga leaders visit on Saturday.
Los Blancos snatched a thrilling 3-2 victory over Manchester City in the Champions League play-off round on Tuesday and host the Premier League champions on Wednesday in the second leg.
In between Carlo Ancelotti's side, leading Atletico Madrid by a point and Barcelona by two at the top of the table, face a tough test at El Sadar.
The 2023 Copa del Rey runners-up are ninth in the league but often rise to the occasion when Spain's biggest sides arrive in Pamplona.
In September Osasuna romped to a 4-2 victory over Barcelona, inflicting what was the Catalans' first league defeat of the season.
Croatian striker Budimir netted twice and with 12 goals trails only Barcelona duo Robert Lewandowski and Raphinha, and Madrid's Kylian Mbappe in the standings.
In January Budimir became Osasuna's record overseas goalscorer and has netted 62 for the club since first arriving on loan in the 2020-21 season from Mallorca, before signing permanently.
Budimir, 33, netted a brace against Real Sociedad in February to earn his team an impressive victory at El Sadar which ended a nine-game winless run in LaLiga.
"(Budimir) is making history, he's doing his thing and he keeps doing it, he's not going to stop," said Osasuna coach Vicente Moreno.
"He works hard every day and can go in (good or bad) runs of form, but he's a player who has earned his place and for us it's great he's putting them away."
The preceding negative streak was started by a 4-0 defeat by Real Madrid at the Santiago Bernabeu, which Osasuna will try and avenge on Saturday.
PLAYERS UNAVAILABLE
Madrid have a raft of defenders unavailable through injury, with Budimir hoping to capitalise as Erling Haaland did for City in midweek with a brace.
However Osasuna will also be missing suspended key centre-back Flavien Boyomo, who scored their late equaliser on Monday which earned them a 1-1 draw at Mallorca.
"We got one point and now we have to think about the ones we didn't get, and win them against Madrid, which is not easy either," said Moreno.
His counterpart Ancelotti warned that Los Blancos were improving and had finally found their path.
The Italian complained frequently in the first half of the season that Real Madrid lacked the right balance, encouraging his attackers to track back and work hard.
"The quality of this team is never in doubt – this is the way forward," said Ancelotti after Madrid's stunning late comeback against Man City.
"This is where the season really starts."
Atletico Madrid play immediately afterwards at home against Celta Vigo, while Barcelona are not in action until Monday, when they host high-flying Rayo Vallecano.
Player to watch: Javi Guerra
Valencia midfielder Guerra has been a key figure under new coach Carlos Corberan. The 21-year-old Spaniard has hit form in recent weeks and played an important role in the team's recent improvement. His work-rate could prove essential in the derby clash against Villarreal on Saturday as Los Che try to climb away from danger.
Key stats
2 - Mallorca's Vedat Muriqi and Valladolid's Mario Martin have each been dismissed twice this season
37 - Despite sitting in mid-table only two teams have conceded more goals than Celta Vigo
1 984 - Barca defender Pau Cubarsi has the most touches in LaLiga