Messi left the jersey vacant by joining Paris Saint Germain on an initial two-year deal last month after Barcelona failed to put together the needed financial package to retain his services.
The six-time Ballon d’or winner wore the jersey for 13 seasons, having taking over from another former Ballon d’or winner, Ronaldinho, in 2008.
The baton has now been passed on to Fati, who like Messi, is a graduate of Barcelona’s famed La Masia academy.
Fati has been with Barcelona’s first team since 2019 and has made 43 appearances for the club, scoring 13 goals and producing five assists.
The 18-year-old Spain international suffered a serious knee injury early last season but has since returned to full training.
"Ansu Fati has a new shirt number. After wearing the number 22 then 17, the young Barça striker will proudly wear the number 10 shirt -- a famous jersey previously worn by legends such as Leo Messi, Ronaldinho and Rivaldo," Barcelona said in a statement.
"Despite being just 18 years of age and still recovering from injury, Ansu Fati forms part of Barça's history as a record breaker and also with the Spanish national side," it added.
Messi made 778 appearances for Barcelona after making his debut in 2003 and is the club’s all-time top scorer with 672 goals. He won 35 trophies with the club including four UEFA Champions League trophies and 10 La Liga titles.
