The Argentine international suffered the strain on Saturday during City's 6-3 win at home to Arsenal in the Premier League.
When asked how long Aguero would be out of action for, Pellegrini told reporters: "At least one month."
The forward has scored 19 goals in 20 games for City so far this season, including 13 in the league.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Liverpool | 10 | 8 | 1 | 1 | 19 | 6 | 13 | 25 |
| 2 | Manchester CityMan City | 10 | 7 | 2 | 1 | 21 | 11 | 10 | 23 |
| 3 | Nottingham ForestNott'm Forest | 10 | 5 | 4 | 1 | 14 | 7 | 7 | 19 |
| 4 | Chelsea | 10 | 5 | 3 | 2 | 20 | 12 | 8 | 18 |
| 5 | Arsenal | 10 | 5 | 3 | 2 | 17 | 11 | 6 | 18 |
| 6 | Aston Villa | 10 | 5 | 3 | 2 | 17 | 15 | 2 | 18 |
| 7 | Tottenham HotspurSpurs | 10 | 5 | 1 | 4 | 22 | 11 | 11 | 16 |
| 8 | Brighton & Hove AlbionBrighton | 10 | 4 | 4 | 2 | 17 | 14 | 3 | 16 |
| 9 | Fulham | 10 | 4 | 3 | 3 | 14 | 13 | 1 | 15 |
| 10 | Bournemouth | 10 | 4 | 3 | 3 | 13 | 12 | 1 | 15 |
| 11 | Newcastle UnitedNewcastle | 10 | 4 | 3 | 3 | 10 | 10 | 0 | 15 |
| 12 | Brentford | 10 | 4 | 1 | 5 | 19 | 20 | -1 | 13 |
| 13 | Manchester UnitedMan Utd | 10 | 3 | 3 | 4 | 9 | 12 | -3 | 12 |
| 14 | West Ham UnitedWest Ham | 10 | 3 | 2 | 5 | 13 | 19 | -6 | 11 |
| 15 | Leicester CityLeicester | 10 | 2 | 4 | 4 | 14 | 18 | -4 | 10 |
| 16 | Everton | 10 | 2 | 3 | 5 | 10 | 17 | -7 | 9 |
| 17 | Crystal Palace | 10 | 1 | 4 | 5 | 8 | 13 | -5 | 7 |
| 18 | Ipswich TownIpswich | 10 | 0 | 5 | 5 | 10 | 21 | -11 | 5 |
| 19 | Southampton | 10 | 1 | 1 | 8 | 7 | 19 | -12 | 4 |
| 20 | Wolverhampton WanderersWolves | 10 | 0 | 3 | 7 | 14 | 27 | -13 | 3 |
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