The Argentine was brought off in the 25th minute against Crystal Palace following a heavy challenge from Scott Dann, while footage on social medial after the game showed the 27-year-old walking with a visible limp.
Keeping you updated - I had studies done today, to be completed tomorrow. We'll have a clearer picture then. Thanks for the support!— Sergio Kun Aguero (@aguerosergiokun) September 13, 2015
Aguero underwent initial tests on Sunday but requires further analysis on Monday.
The news is blow for City, who could also be without David Silva for their Champions League group-stage opener at home to Juventus on Tuesday evening. The Spaniard missed the match against Palace due to an ankle problem.
Kelechi Iheanacho’s injury-time strike sealed a 1-0 win for City at Selhurst Park on Saturday, which has kept Manuel Pellegrini’s side four points clear at the top of the Premier League, and 11 ahead of champions Chelsea, who were beaten by Everton at Goodison Park.