Athletic Bilbao is the first Spanish side in action in this season's Champions League, with the Basque outfit hosting Arsenal on Tuesday evening.

Real Madrid's Antonio Rudiger (R) vies with Athletic Bilbao's Gorka Guruzeta during the Spanish La Liga football match between Real Madrid and Athletic Bilbao in Madrid, Spain, on April 20, 2025. (Photo by Gustavo Valiente/Xinhua)

Athletic returns to the competition after 11 years and faces a difficult rival in big-spending Arsenal, which has signed players such as Viktor Gyokeres, Eberechi Eze and Noni Madueke over the summer to completely revamp its attack.

Bukayo Saka and Martin Odegaard will miss the trip to the San Mames Stadium through injury but Arsenal's easy win over Nottingham Forest on Saturday underlined the task facing Athletic.

Ernesto Valverde's side suffered a surprise defeat at home to Alaves on Saturday to end its 100 percent start to the new La Liga season, and the coach needs to see a major improvement.

Athletic is without star player Nico Williams with a groin injury picked up on international duty, and Valverde has to decide whether Alex Berenguer or Robert Navarro plays on the left wing, while Benat Prados' knee problems limit his options in defence, and Aymeric Laporte is still short of match fitness after his late arrival from Al Nassr.

San Mames should be familiar territory to Arsenal coach Mikel Arteta, who played for local rival Real Sociedad, while Arsenal midfielders Mikel Merino and Martin Zubimendi both joined Arsenal from the San Sebastian-based club.

Meanwhile, Arsenal's reserve goalkeeper Kepa Arrizabalaga returns for the first time to the club where he began his career before making a record-breaking move to Chelsea in 2018.

Real Madrid also starts its Champions League campaign on Tuesday, with Xabi Alonso's side expected to continue its perfect start to the season with a home game against Olympique Marseille.

Alonso has so far made subtle changes to his side for home and away fixtures and Trent Alexander-Arnold and Fede Valverde will probably return to his starting 11 against the French outfit.

Meanwhile, Kylian Mbappe will continue to lead the Real Madrid attack after his excellent start to the season.