The 26-year-old had been without a club since leaving Bristol City at the end of last season, but will now spend the next three months at Valley Parade.
The centre-back will primarily act as cover for Andrew Davies, who has been ruled out until the New Year following knee surgery.
Bates made more than 100 league appearances during his time with Middlesbrough, before leaving for Bristol City in 2012.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Port Vale | 14 | 9 | 3 | 2 | 23 | 15 | 8 | 30 |
| 2 | Walsall | 13 | 8 | 2 | 3 | 26 | 14 | 12 | 26 |
| 3 | Notts County | 14 | 7 | 5 | 2 | 22 | 12 | 10 | 26 |
| 4 | Doncaster RoversDoncaster | 14 | 8 | 2 | 4 | 20 | 16 | 4 | 26 |
| 5 | Crewe AlexandraCrewe | 13 | 7 | 3 | 3 | 16 | 12 | 4 | 24 |
| 6 | Chesterfield | 14 | 5 | 7 | 2 | 28 | 15 | 13 | 22 |
| 7 | Bradford CityBradford | 14 | 6 | 4 | 4 | 20 | 15 | 5 | 22 |
| 8 | MK Dons | 14 | 6 | 3 | 5 | 21 | 16 | 5 | 21 |
| 9 | BarrowBarrow | 14 | 6 | 3 | 5 | 15 | 11 | 4 | 21 |
| 10 | Grimsby Town | 14 | 7 | 0 | 7 | 18 | 25 | -7 | 21 |
| 11 | Gillingham | 14 | 6 | 2 | 6 | 15 | 12 | 3 | 20 |
| 12 | Salford City | 14 | 5 | 5 | 4 | 14 | 16 | -2 | 20 |
| 13 | AFC Wimbledon | 11 | 6 | 1 | 4 | 18 | 9 | 9 | 19 |
| 14 | Newport CountyNewport | 14 | 6 | 1 | 7 | 18 | 24 | -6 | 19 |
| 15 | Fleetwood TownFleetwood | 13 | 4 | 6 | 3 | 19 | 15 | 4 | 18 |
| 16 | Cheltenham TownCheltenham | 14 | 5 | 2 | 7 | 18 | 21 | -3 | 17 |
| 17 | Harrogate TownHarrogate | 14 | 4 | 3 | 7 | 11 | 19 | -8 | 15 |
| 18 | Bromley | 13 | 3 | 5 | 5 | 15 | 17 | -2 | 14 |
| 19 | Tranmere RoversTranmere | 13 | 3 | 5 | 5 | 8 | 16 | -8 | 14 |
| 20 | Accrington StanleyAccrington | 13 | 3 | 4 | 6 | 15 | 22 | -7 | 13 |
| 21 | Colchester UnitedColchester | 13 | 2 | 6 | 5 | 16 | 20 | -4 | 12 |
| 22 | Swindon TownSwindon | 14 | 2 | 6 | 6 | 15 | 20 | -5 | 12 |
| 23 | Carlisle UnitedCarlisle | 14 | 2 | 2 | 10 | 12 | 28 | -16 | 8 |
| 24 | Morecambe | 14 | 1 | 4 | 9 | 12 | 25 | -13 | 7 |
| > League Two Full Table | |||||||||
