The Mexico international spent last season on loan with the Portuguese club, for whom he made 27 league appearances.
Layun's performances were good enough to convince the Porto hierarchy to turn the switch into a permanent one for a fee believed to be around £4m.
It is thought that Watford have negotiated a 20% sell-on clause as part of the deal.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Leeds UnitedLeeds | 38 | 23 | 11 | 4 | 76 | 25 | 51 | 80 |
| 2 | Sheffield UnitedSheff Utd | 38 | 25 | 7 | 6 | 53 | 28 | 25 | 80 |
| 3 | Burnley | 38 | 21 | 15 | 2 | 52 | 11 | 41 | 78 |
| 4 | Sunderland | 38 | 19 | 12 | 7 | 55 | 37 | 18 | 69 |
| 5 | Coventry CityCoventry | 38 | 17 | 8 | 13 | 55 | 48 | 7 | 59 |
| 6 | West Bromwich AlbionWest Brom | 38 | 13 | 18 | 7 | 48 | 34 | 14 | 57 |
| 7 | Bristol City | 38 | 14 | 15 | 9 | 49 | 41 | 8 | 57 |
| 8 | Middlesbrough | 38 | 15 | 9 | 14 | 57 | 48 | 9 | 54 |
| 9 | Blackburn RoversBlackburn | 38 | 15 | 7 | 16 | 42 | 40 | 2 | 52 |
| 10 | Watford | 38 | 15 | 7 | 16 | 47 | 51 | -4 | 52 |
| 11 | Millwall | 38 | 13 | 12 | 13 | 37 | 39 | -2 | 51 |
| 12 | Sheffield WednesdaySheff Weds | 38 | 14 | 9 | 15 | 53 | 59 | -6 | 51 |
| 13 | Norwich CityNorwich | 38 | 12 | 13 | 13 | 60 | 54 | 6 | 49 |
| 14 | Preston North EndPreston | 38 | 10 | 17 | 11 | 39 | 44 | -5 | 47 |
| 15 | Queens Park RangersQPR | 38 | 11 | 12 | 15 | 44 | 50 | -6 | 45 |
| 16 | Swansea CitySwansea | 38 | 12 | 8 | 18 | 38 | 49 | -11 | 44 |
| 17 | Portsmouth | 38 | 11 | 9 | 18 | 46 | 61 | -15 | 42 |
| 18 | Oxford UnitedOxford Utd | 38 | 10 | 12 | 16 | 39 | 55 | -16 | 42 |
| 19 | Hull City | 38 | 10 | 11 | 17 | 39 | 47 | -8 | 41 |
| 20 | Stoke CityStoke | 38 | 9 | 12 | 17 | 37 | 51 | -14 | 39 |
| 21 | Cardiff CityCardiff | 38 | 9 | 12 | 17 | 42 | 62 | -20 | 39 |
| 22 | Derby CountyDerby | 38 | 10 | 8 | 20 | 40 | 51 | -11 | 38 |
| 23 | Luton TownLuton | 38 | 9 | 8 | 21 | 34 | 60 | -26 | 35 |
| 24 | Plymouth ArgylePlymouth | 38 | 7 | 12 | 19 | 40 | 77 | -37 | 33 |
| > Championship Full Table | |||||||||
