He would make his first-team debut during a 2002–03 UEFA Champions League match against Galatasaray SK, a 3–1 home victory where he came on as a late substitute for Frank de Boer.

Oleguer started the match, but on the day he appeared tense and slow, struggling to neutralise Freddie Ljungberg's runs down the wing and more importantly not being able to stop Sol Campbell scoring the opening goal.

[12] He also spoke out against the banning of the Catalan national team by the Royal Spanish Football Federation, when the former was scheduled to play a friendly against the United States in conjunction with FIFA-recognised international fixtures in that same week.

[14] He was operated on but he spent six weeks on the sidelines, and he took almost no part in the team's campaign overall;[15] Barcelona finished third, and his only competitive goal took place on 24 April 2005 when he opened the 4–0 away defeat of Málaga CF.

[5] On 30 March 2006 he published his first book with recollections on his youth, early career and the league triumph of 2004–05 (and the subsequent street parade through the Avinguda Diagonal in Barcelona).

The book, called Camí d'Itaca (The Road to Ithaca), dealt with such varied subjects as childhood anorexia, the anti-fascist struggle and the previous Spanish government's involvement in both Gulf Wars.

[5] Oleguer had sympathies with left wing and Catalan nationalist causes, and was asked by Subcomandante Marcos of the Zapatista Army of National Liberation to play a charity match in Chiapas, Mexico, during the summer of 2005.

His decision to write the article brought veiled criticism at Barcelona, both from coach Rijkaard and president Joan Laporta, as well as earning him disrespectful remarks from fellow professional Salva Ballesta, known for his Francoist views.

[30] He also became the subject of a strong public backlash among some elements in Spain, and was regularly heckled and booed in some of the country's football stadiums due to the article and his pro-Catalan independence stance.