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 | Gillingham | 9 | 6 | 1 | 2 | 12 | 3 | 9 | 19 |
| 2 | Notts County | 9 | 5 | 3 | 1 | 17 | 8 | 9 | 18 |
| 3 | Walsall | 9 | 6 | 0 | 3 | 17 | 10 | 7 | 18 |
| 4 | BarrowBarrow | 9 | 5 | 1 | 3 | 11 | 6 | 5 | 16 |
| 5 | Doncaster RoversDoncaster | 9 | 5 | 1 | 3 | 12 | 12 | 0 | 16 |
| 6 | Fleetwood TownFleetwood | 8 | 4 | 3 | 1 | 16 | 9 | 7 | 15 |
| 7 | Port Vale | 9 | 4 | 3 | 2 | 14 | 12 | 2 | 15 |
| 8 | Grimsby Town | 9 | 5 | 0 | 4 | 13 | 14 | -1 | 15 |
| 9 | Newport CountyNewport | 9 | 5 | 0 | 4 | 15 | 17 | -2 | 15 |
| 10 | Chesterfield | 9 | 3 | 4 | 2 | 15 | 8 | 7 | 13 |
| 11 | AFC Wimbledon | 6 | 4 | 1 | 1 | 9 | 4 | 5 | 13 |
| 12 | Crewe AlexandraCrewe | 8 | 4 | 1 | 3 | 8 | 9 | -1 | 13 |
| 13 | Bradford CityBradford | 9 | 3 | 3 | 3 | 11 | 10 | 1 | 12 |
| 14 | MK Dons | 9 | 3 | 2 | 4 | 12 | 11 | 1 | 11 |
| 15 | Colchester UnitedColchester | 9 | 2 | 4 | 3 | 13 | 15 | -2 | 10 |
| 16 | Cheltenham TownCheltenham | 9 | 3 | 1 | 5 | 11 | 14 | -3 | 10 |
| 17 | Tranmere RoversTranmere | 8 | 2 | 4 | 2 | 4 | 8 | -4 | 10 |
| 18 | Harrogate TownHarrogate | 9 | 3 | 1 | 5 | 9 | 16 | -7 | 10 |
| 19 | Bromley | 9 | 2 | 3 | 4 | 12 | 14 | -2 | 9 |
| 20 | Salford City | 8 | 2 | 3 | 3 | 5 | 9 | -4 | 9 |
| 21 | Swindon TownSwindon | 9 | 1 | 4 | 4 | 9 | 13 | -4 | 7 |
| 22 | Carlisle UnitedCarlisle | 9 | 2 | 0 | 7 | 10 | 19 | -9 | 6 |
| 23 | Morecambe | 9 | 0 | 4 | 5 | 7 | 12 | -5 | 4 |
| 24 | Accrington StanleyAccrington | 8 | 0 | 3 | 5 | 9 | 18 | -9 | 3 |
| > League Two Full Table | |||||||||
