Aguero bid a tearful goodbye to the beautiful game on Wednesday at Barcelona’s Camp Nou stadium.
The former Atletico Madrid striker's final game came against Deportivo Alaves on October 30, when he was substituted on the cusp of halftime with chest complaints.
He was initially ruled out for three months but one of the most prolific strikers in the 21st century will not be returning to the field.
Aguero and Messi enjoyed so many good moments in the colours of the junior and senior Argentina sides which culminated in Copa America glory this summer.
In a heartfelt tribute to Manchester City's all-time top scorer, Messi wrote: "Practically a whole career together, Kun... We lived very beautiful moments and others that were not so [beautiful], all of them made us unite more and more and made us greater friends. And we are going to continue living [beautiful moments] together off the pitch.
"With the great joy of lifting the Copa America so recently, with all the achievements you achieved in England…the truth is that now it hurts a lot to see how you have to stop doing what you love the most because of what happened to you.
"Surely you will continue to be happy because you are a person who transmits happiness, and those of us who love you will be with you.
"Now a new stage of your life begins and I am convinced you are going to live it with a smile and with all the enthusiasm that you put into everything.
"All the best in this new stage!!! I love you a lot, my friend, I'm going to miss being with you on the pitch with the National Team a lot!"
