The deal runs until January 2 and does not include a clause allowing Birmingham to recall the 29-year-old, who is in the last year of his contract at St Andrew's.
Duffy joined Birmingham from Doncaster Rovers a year ago, but made just one Championship start in his debut campaign.
He also had a brief loan spell in League One with Chesterfield in February earlier this year.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| C | Leicester CityLeicester | 46 | 31 | 4 | 11 | 89 | 41 | 48 | 97 |
| P | Ipswich TownIpswich | 46 | 28 | 12 | 6 | 92 | 57 | 35 | 96 |
| 3 | Leeds UnitedLeeds | 46 | 27 | 9 | 10 | 81 | 43 | 38 | 90 |
| 4 | Southampton | 46 | 26 | 9 | 11 | 87 | 63 | 24 | 87 |
| 5 | West Bromwich AlbionWest Brom | 46 | 21 | 12 | 13 | 70 | 47 | 23 | 75 |
| 6 | Norwich CityNorwich | 46 | 21 | 10 | 15 | 79 | 64 | 15 | 73 |
| 7 | Hull City | 46 | 19 | 13 | 14 | 68 | 60 | 8 | 70 |
| 8 | Middlesbrough | 46 | 20 | 9 | 17 | 71 | 62 | 9 | 69 |
| 9 | Coventry CityCoventry | 46 | 17 | 13 | 16 | 70 | 59 | 11 | 64 |
| 10 | Preston North EndPreston | 46 | 18 | 9 | 19 | 56 | 67 | -11 | 63 |
| 11 | Bristol City | 46 | 17 | 11 | 18 | 53 | 51 | 2 | 62 |
| 12 | Cardiff CityCardiff | 46 | 19 | 5 | 22 | 53 | 70 | -17 | 62 |
| 13 | Millwall | 46 | 16 | 11 | 19 | 45 | 55 | -10 | 59 |
| 14 | Swansea CitySwansea | 46 | 15 | 12 | 19 | 59 | 65 | -6 | 57 |
| 15 | Watford | 46 | 13 | 17 | 16 | 61 | 61 | 0 | 56 |
| 16 | Sunderland | 46 | 16 | 8 | 22 | 52 | 54 | -2 | 56 |
| 17 | Stoke CityStoke | 46 | 15 | 11 | 20 | 49 | 60 | -11 | 56 |
| 18 | Queens Park RangersQPR | 46 | 15 | 11 | 20 | 47 | 58 | -11 | 56 |
| 19 | Blackburn RoversBlackburn | 46 | 14 | 11 | 21 | 60 | 74 | -14 | 53 |
| 20 | Sheffield WednesdaySheff Weds | 46 | 15 | 8 | 23 | 44 | 68 | -24 | 53 |
| 21 | Plymouth ArgylePlymouth | 46 | 13 | 12 | 21 | 59 | 70 | -11 | 51 |
| R | Birmingham CityBirmingham | 46 | 13 | 11 | 22 | 50 | 65 | -15 | 50 |
| R | Huddersfield TownHuddersfield | 46 | 9 | 18 | 19 | 48 | 77 | -29 | 45 |
| R | Rotherham UnitedRotherham | 46 | 5 | 12 | 29 | 37 | 89 | -52 | 27 |
| > Championship Full Table | |||||||||
