The Brazilian football federation (CBF) has confirmed the forward reported a problem after playing in City's season-opening Premier League victory at Wolves on Monday.
The news is a serious blow for City, who are currently without record goalscorer Sergio Aguero, as well as a host of other players.
In addition, Ilkay Gundogan is isolating after contracting coronavirus and defender Aymeric Laporte is unlikely to be fit to return after his recent positive test for Covid-19.
The Brazilian's absence leaves City particularly light up front ahead of Sunday's Premier League game against Leicester.
Speaking after Thursday's Carabao Cup victory over Bournemouth, City manager Pep Guardiola said: "The situation we have right now, we have just 13 players available in the first team."