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 | Liverpool | 11 | 9 | 1 | 1 | 21 | 6 | 15 | 28 |
| 2 | Manchester CityMan City | 11 | 7 | 2 | 2 | 22 | 13 | 9 | 23 |
| 3 | Chelsea | 11 | 5 | 4 | 2 | 21 | 13 | 8 | 19 |
| 4 | Arsenal | 11 | 5 | 4 | 2 | 18 | 12 | 6 | 19 |
| 5 | Nottingham ForestNott'm Forest | 11 | 5 | 4 | 2 | 15 | 10 | 5 | 19 |
| 6 | Brighton & Hove AlbionBrighton | 11 | 5 | 4 | 2 | 19 | 15 | 4 | 19 |
| 7 | Fulham | 11 | 5 | 3 | 3 | 16 | 13 | 3 | 18 |
| 8 | Newcastle UnitedNewcastle | 11 | 5 | 3 | 3 | 13 | 11 | 2 | 18 |
| 9 | Aston Villa | 11 | 5 | 3 | 3 | 17 | 17 | 0 | 18 |
| 10 | Tottenham HotspurSpurs | 11 | 5 | 1 | 5 | 23 | 13 | 10 | 16 |
| 11 | Brentford | 11 | 5 | 1 | 5 | 22 | 22 | 0 | 16 |
| 12 | Bournemouth | 11 | 4 | 3 | 4 | 15 | 15 | 0 | 15 |
| 13 | Manchester UnitedMan Utd | 11 | 4 | 3 | 4 | 12 | 12 | 0 | 15 |
| 14 | West Ham UnitedWest Ham | 11 | 3 | 3 | 5 | 13 | 19 | -6 | 12 |
| 15 | Leicester CityLeicester | 11 | 2 | 4 | 5 | 14 | 21 | -7 | 10 |
| 16 | Everton | 11 | 2 | 4 | 5 | 10 | 17 | -7 | 10 |
| 17 | Ipswich TownIpswich | 11 | 1 | 5 | 5 | 12 | 22 | -10 | 8 |
| 18 | Crystal Palace | 11 | 1 | 4 | 6 | 8 | 15 | -7 | 7 |
| 19 | Wolverhampton WanderersWolves | 11 | 1 | 3 | 7 | 16 | 27 | -11 | 6 |
| 20 | Southampton | 11 | 1 | 1 | 9 | 7 | 21 | -14 | 4 |
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