The Spaniard, who scored Chelsea's goal in Naples, is believed to have suffered the injury following a first-half collision with Napoli defender Salvatore Aronica.
When asked about Mata's complaint, Chelsea manager Andre Villas-Boas told reporters: "We have to check it. Maybe it is broken."
Mata is now expected to undergo a series of tests to determine the extent of the problem.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Manchester CityMan City | 4 | 4 | 0 | 0 | 11 | 3 | 8 | 12 |
| 2 | Arsenal | 4 | 3 | 1 | 0 | 6 | 1 | 5 | 10 |
| 3 | Newcastle UnitedNewcastle | 4 | 3 | 1 | 0 | 6 | 3 | 3 | 10 |
| 4 | Liverpool | 4 | 3 | 0 | 1 | 7 | 1 | 6 | 9 |
| 5 | Aston Villa | 4 | 3 | 0 | 1 | 7 | 6 | 1 | 9 |
| 6 | Brighton & Hove AlbionBrighton | 4 | 2 | 2 | 0 | 6 | 2 | 4 | 8 |
| 7 | Nottingham ForestNott'm Forest | 4 | 2 | 2 | 0 | 4 | 2 | 2 | 8 |
| 8 | Chelsea | 4 | 2 | 1 | 1 | 8 | 5 | 3 | 7 |
| 9 | Brentford | 4 | 2 | 0 | 2 | 6 | 6 | 0 | 6 |
| 10 | Manchester UnitedMan Utd | 4 | 2 | 0 | 2 | 5 | 5 | 0 | 6 |
| 11 | Bournemouth | 4 | 1 | 2 | 1 | 5 | 5 | 0 | 5 |
| 12 | Fulham | 4 | 1 | 2 | 1 | 4 | 4 | 0 | 5 |
| 13 | Tottenham HotspurSpurs | 4 | 1 | 1 | 2 | 6 | 4 | 2 | 4 |
| 14 | West Ham UnitedWest Ham | 4 | 1 | 1 | 2 | 5 | 6 | -1 | 4 |
| 15 | Leicester CityLeicester | 4 | 0 | 2 | 2 | 5 | 7 | -2 | 2 |
| 16 | Crystal Palace | 4 | 0 | 2 | 2 | 4 | 7 | -3 | 2 |
| 17 | Ipswich TownIpswich | 4 | 0 | 2 | 2 | 2 | 7 | -5 | 2 |
| 18 | Wolverhampton WanderersWolves | 4 | 0 | 1 | 3 | 4 | 11 | -7 | 1 |
| 19 | Southampton | 4 | 0 | 0 | 4 | 1 | 8 | -7 | 0 |
| 20 | Everton | 4 | 0 | 0 | 4 | 4 | 13 | -9 | 0 |
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