The ex-Spain international came through the youth system at Osasuna before making the move to Malaga in 2011, where his form attracted the interest of Arsenal.
Monreal had already witnessed teammate and compatriot Santi Cazorla sign for the Gunners in the summer of 2012, and he made the move to the Emirates a few months later.
Despite initially struggling to win over the fans in North London, Monreal eventually established a reputation as one of Arsenal's most consistent performers as he battled Kieran Gibbs for the left-back spot.
The Spaniard cemented his place as Arsenal's first-choice left-back from the 2014-15 season onwards and spent six-and-a-half years in North London before returning to his homeland with Real Sociedad.
Monreal was a key fixture under Imanol Alguacil during the 2019-20 and 2020-21 campaigns, featuring prominently in La Liga and Europa League action.
However, the defender did not play a single minute of the 2021-22 season due to a knee injury, and he has now called time on his professional career.
Confirming his retirement with a heartfelt message on social media, Monreal affirmed that he 'accepted' the situation with his knee injury and is grateful for the success he enjoyed as a player.
"36 years playing football. 16 as a professional. Squeezing my body and taking it to limits that I would never have imagined," the left-back wrote.
"My knee sends me a message... loud and clear; I cannot continue! Do I get mad? NO! I listen to it and accept the situation and thank it for everything.
"A stage is over. Another starts. I'm happy and feeling good. One more time... I FEEL GOOD!!! And that gives me peace of mind. Life is a gift and I like to be grateful. Thank you @caosasuna @rfef @malagacf @arsenal @realsociedad for letting me cross your paths. What a good years...."
During his time at Arsenal, Monreal posted a total of 10 goals and 20 assists in 251 games for the Gunners, featuring under Arsene Wenger and Unai Emery before leaving in the summer of 2019.
Monreal won three FA Cups and three Community Shields with the Gunners and collected his final piece of silverware as a player with Sociedad in 2019-20, winning the Copa del Rey.
The left-back contributed one goal and four assists in 69 outings for Sociedad in all competitions and earned 22 caps for the Spain national team, scoring once and providing four assists.
Monreal only made one major tournament appearance for Spain in the 2013 Confederations Cup, and he was an unused substitute for La Roja during the 2018 World Cup.