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 | |
| C | Stockport CountyStockport | 45 | 27 | 11 | 7 | 95 | 46 | 49 | 92 |
| P | Mansfield TownMansfield | 45 | 24 | 13 | 8 | 89 | 46 | 43 | 85 |
| P | Wrexham | 45 | 25 | 10 | 10 | 87 | 51 | 36 | 85 |
| 4 | MK Dons | 45 | 23 | 8 | 14 | 79 | 64 | 15 | 77 |
| 5 | Doncaster RoversDoncaster | 45 | 21 | 7 | 17 | 71 | 66 | 5 | 70 |
| 6 | Crewe AlexandraCrewe | 45 | 19 | 13 | 13 | 68 | 64 | 4 | 70 |
| 7 | BarrowBarrow | 45 | 18 | 14 | 13 | 61 | 55 | 6 | 68 |
| 8 | Crawley TownCrawley | 45 | 20 | 7 | 18 | 71 | 67 | 4 | 67 |
| 9 | Bradford CityBradford | 45 | 18 | 12 | 15 | 57 | 58 | -1 | 66 |
| 10 | Walsall | 45 | 18 | 11 | 16 | 68 | 68 | 0 | 65 |
| 11 | Gillingham | 45 | 18 | 9 | 18 | 44 | 55 | -11 | 63 |
| 12 | AFC Wimbledon | 45 | 16 | 14 | 15 | 59 | 50 | 9 | 62 |
| 13 | Harrogate TownHarrogate | 45 | 17 | 11 | 17 | 58 | 67 | -9 | 62 |
| 14 | Notts County | 45 | 18 | 7 | 20 | 89 | 85 | 4 | 61 |
| 15 | Tranmere RoversTranmere | 45 | 17 | 6 | 22 | 66 | 66 | 0 | 57 |
| 16 | Morecambe | 45 | 17 | 9 | 19 | 64 | 78 | -14 | 57 |
| 17 | Newport CountyNewport | 45 | 16 | 7 | 22 | 61 | 72 | -11 | 55 |
| 18 | Accrington StanleyAccrington | 45 | 15 | 9 | 21 | 59 | 70 | -11 | 54 |
| 19 | Swindon TownSwindon | 45 | 14 | 11 | 20 | 74 | 80 | -6 | 53 |
| 20 | Salford City | 45 | 13 | 11 | 21 | 64 | 80 | -16 | 50 |
| 21 | Grimsby Town | 45 | 11 | 16 | 18 | 57 | 72 | -15 | 49 |
| 22 | Colchester UnitedColchester | 45 | 11 | 11 | 23 | 58 | 79 | -21 | 44 |
| 23 | Sutton UnitedSutton | 45 | 9 | 14 | 22 | 55 | 80 | -25 | 41 |
| R | Forest Green RoversForest Green | 45 | 10 | 9 | 26 | 43 | 78 | -35 | 39 |
| > League Two Full Table | |||||||||
