Nomoko, 17, tore the ligament in his right knee in last week's UEFA Youth League win over Eintracht Frankfurt. He also suffered an associated meniscus injury in the same knee.
The teenage winger subsequently underwent an operation on Tuesday, with Barça announcing Wednesday his expected recovery time "will be around 12 months."
Nomoko has been at Barça since he was eight years old, first joining the club in 2016 before progressing through the academy until being promoted to the B team, who play in the fourth tier of Spanish football, this past summer.
He quickly became a key player for Juliano Belletti's side, scoring two goals and providing four assists in 14 appearances this season despite being one of the youngest players on the team.
In parallel, he also featured in four games for the U19s in the Youth League, helping Barça ease through to the knockout rounds of the prestigious youth competition.
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Born in Mali, Nomoko moved to Catalonia as a child and is a youth international for Spain.
Barça have high hopes for him given his speed, one-on-one skills and ability to play on either wing.
