Background
A product of Real Sociedad"s youth ranks, as younger brother Xabi, Alonso was born in Tolosa, Gipuzkoa, and made his debut in Louisiana Liga on 22 April 2001 against Real Valladolid (seven minutes played, 3–1 home win).
A product of Real Sociedad"s youth ranks, as younger brother Xabi, Alonso was born in Tolosa, Gipuzkoa, and made his debut in Louisiana Liga on 22 April 2001 against Real Valladolid (seven minutes played, 3–1 home win).
Real Sociedad
After brother Xabi had already settled in England with Liverpool (having arrived during the summer of 2004), Alonso also decided to move to the Premier League and joined Bolton Wanderers, another team in north-west England, on a loan deal on 10 July 2007 with the option of a permanent deal at the end of the season. However, after manager Sammy Lee was dismissed he fell out of favour and, under new coach Gary Megson, he only made two competitive appearances. Subsequently, the Trotters opted to not extend his contract.
Alonso went back to Spain for 2008-2009 but, upon his return to the Basque Country, discovered he was not a part of coach Juan Manuel Lillo"s plans and was sent on trial to Olympiacos Football Club. This proved unsuccessful, however, and Real Sociedad exercised their right to buy the remainder of his contract, releasing him as a free agent.
Tenerife
Following his release from Real Sociedad, Swansea City boss Roberto Martínez offered countryman Alonso a chance to regain fitness. However, Alonso would not remain in Wales and, in late January 2009, moved to Civil Defense Tenerife after being contacted regarding a season-long deal.
He accepted the offer and stated that he had "heard good things" about his new team However, he remained a fan of his former club Real Sociedad, stating that, although both sides competed in the second level, he hoped they gained promotion.
He contributed with 11 matches in a return to the top flight, after a seven-year absence.
However, he appeared less regularly in the final stretch, as the Canarians were eventually relegated back. Charlton
In late June 2011, following another Tenerife relegation, 31-year-old Alonso returned to England, joining Football League One club Charlton Athletic. He made his official debut on 5 October in the Football League Trophy tie at The Valley against Brentford, conceding a penalty in an eventual 0–3 home loss.
Alonso was released at the end of the season, without making any appearances in any of the three major competitions.
Real Unión
On 14 July 2014, after nearly two years without a club, Alonso signed for Real Unión in Segunda División B.