The 25-year-old Jamaican, who is a product of the Hornets' youth academy, impressed Royals boss Brian McDermott with a string of solid performances last season.
The newly-promoted Berkshire club have offered Watford £2m for the player and that has been rejected, according to Sky Sports News.
Mariappa has made 247 appearances for Watford in seven seasons at Vicarage Road.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Leeds UnitedLeeds | 17 | 10 | 5 | 2 | 31 | 12 | 19 | 35 |
| 2 | Sheffield UnitedSheff Utd | 17 | 11 | 4 | 2 | 24 | 9 | 15 | 35 |
| 3 | Burnley | 17 | 9 | 6 | 2 | 21 | 6 | 15 | 33 |
| 4 | Sunderland | 17 | 9 | 6 | 2 | 26 | 12 | 14 | 33 |
| 5 | Watford | 17 | 9 | 2 | 6 | 26 | 24 | 2 | 29 |
| 6 | Middlesbrough | 17 | 8 | 3 | 6 | 29 | 20 | 9 | 27 |
| 7 | West Bromwich AlbionWest Brom | 17 | 6 | 9 | 2 | 18 | 11 | 7 | 27 |
| 8 | Blackburn RoversBlackburn | 16 | 7 | 4 | 5 | 20 | 17 | 3 | 25 |
| 9 | Millwall | 16 | 6 | 6 | 4 | 19 | 14 | 5 | 24 |
| 10 | Norwich CityNorwich | 17 | 5 | 7 | 5 | 31 | 25 | 6 | 22 |
| 11 | Swansea CitySwansea | 17 | 6 | 4 | 7 | 16 | 15 | 1 | 22 |
| 12 | Bristol City | 17 | 5 | 7 | 5 | 20 | 21 | -1 | 22 |
| 13 | Sheffield WednesdaySheff Weds | 17 | 6 | 4 | 7 | 20 | 26 | -6 | 22 |
| 14 | Stoke CityStoke | 17 | 5 | 6 | 6 | 19 | 20 | -1 | 21 |
| 15 | Derby CountyDerby | 17 | 5 | 5 | 7 | 21 | 22 | -1 | 20 |
| 16 | Luton TownLuton | 17 | 5 | 3 | 9 | 18 | 29 | -11 | 18 |
| 17 | Coventry CityCoventry | 17 | 4 | 5 | 8 | 22 | 25 | -3 | 17 |
| 18 | Oxford UnitedOxford Utd | 17 | 4 | 5 | 8 | 19 | 27 | -8 | 17 |
| 19 | Preston North EndPreston | 17 | 3 | 8 | 6 | 16 | 24 | -8 | 17 |
| 20 | Plymouth ArgylePlymouth | 17 | 4 | 5 | 8 | 18 | 34 | -16 | 17 |
| 21 | Cardiff CityCardiff | 17 | 4 | 4 | 9 | 15 | 26 | -11 | 16 |
| 22 | Hull City | 17 | 3 | 6 | 8 | 16 | 23 | -7 | 15 |
| 23 | Queens Park RangersQPR | 17 | 2 | 8 | 7 | 15 | 26 | -11 | 14 |
| 24 | Portsmouth | 15 | 2 | 6 | 7 | 16 | 28 | -12 | 12 |
| > Championship Full Table | |||||||||
