Alonso has had a magnificent career that spanned 18 years filled with trophies at several clubs that include Liverpool and Real Madrid.
According to German newspaper Sports Bild, the 35-year-old informed Bayern Munich of his decision to retire at the end of the 2016/2017 season.
Although the club has accepted his decision, they are however reportedly kept the door open for the midfielder in the case that he changes his mind.
Alonso started what turned out to be a prolific career with his hometown club Real Sociedad before moving to Premier League side Liverpool in 2004.
At Liverpool, he won the Champions League, FA Cup and Super Cup but the Premier League eluded him.
He returned to Spain in a £30million move to Real in 2009, winning another Champions League title in 2014.
ALSO READ: Alonso gets tax fraud charge
He also won two Copa del Rey titles, the Spanish Super Cup and finally his first league title.
After five years in Madrid, Alonso moved to Munich where he has won two Bundesliga titles, the German Cup and the German Super Cup.
He got his first Spain cap in April 2003 in a 4–0 victory against Ecuador and went to play 114 caps for the one time World champions.
ALSO READ: Alonso missed at Spain national team
With Spain, he won two European Championship and the 2010 FIFA World Cup.