The 26-year-old requires surgery on a knee injury.
"He's having an operation next Wednesday on a cartilage tear," Wilson told BBC Radio Sheffield.
"It's very unlikely that we'll see him again before the end of the season now."
O'Brien has made 27 appearances for Barnsley in the Championship this season, scoring two goals.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Birmingham CityBirmingham | 24 | 17 | 5 | 2 | 42 | 17 | 25 | 56 |
| 2 | Wycombe WanderersWycombe | 26 | 16 | 6 | 4 | 52 | 28 | 24 | 54 |
| 3 | Wrexham | 26 | 15 | 6 | 5 | 38 | 20 | 18 | 51 |
| 4 | Huddersfield TownHuddersfield | 25 | 14 | 6 | 5 | 39 | 21 | 18 | 48 |
| 5 | Barnsley | 26 | 12 | 6 | 8 | 40 | 36 | 4 | 42 |
| 6 | Stockport CountyStockport | 26 | 11 | 8 | 7 | 40 | 28 | 12 | 41 |
| 7 | Reading | 25 | 12 | 5 | 8 | 40 | 36 | 4 | 41 |
| 8 | Leyton Orient | 25 | 11 | 5 | 9 | 32 | 22 | 10 | 38 |
| 9 | Bolton WanderersBolton | 25 | 11 | 5 | 9 | 38 | 39 | -1 | 38 |
| 10 | Mansfield TownMansfield | 24 | 11 | 4 | 9 | 32 | 28 | 4 | 37 |
| 11 | Lincoln CityLincoln | 26 | 9 | 8 | 9 | 29 | 30 | -1 | 35 |
| 12 | Charlton AthleticCharlton | 24 | 9 | 7 | 8 | 29 | 25 | 4 | 34 |
| 13 | Rotherham UnitedRotherham | 25 | 9 | 7 | 9 | 28 | 26 | 2 | 34 |
| 14 | Blackpool | 25 | 7 | 10 | 8 | 34 | 37 | -3 | 31 |
| 15 | Stevenage | 24 | 8 | 7 | 9 | 19 | 22 | -3 | 31 |
| 16 | Exeter CityExeter | 25 | 9 | 4 | 12 | 28 | 32 | -4 | 31 |
| 17 | Wigan AthleticWigan | 24 | 8 | 6 | 10 | 23 | 24 | -1 | 30 |
| 18 | Bristol Rovers | 25 | 8 | 4 | 13 | 25 | 39 | -14 | 28 |
| 19 | Peterborough UnitedPeterborough | 25 | 7 | 5 | 13 | 41 | 46 | -5 | 26 |
| 20 | Northampton TownNorthampton | 26 | 6 | 8 | 12 | 24 | 40 | -16 | 26 |
| 21 | Crawley TownCrawley | 24 | 5 | 6 | 13 | 25 | 44 | -19 | 21 |
| 22 | Shrewsbury TownShrewsbury | 25 | 5 | 5 | 15 | 26 | 45 | -19 | 20 |
| 23 | Cambridge UnitedCambridge | 25 | 4 | 6 | 15 | 24 | 45 | -21 | 18 |
| 24 | Burton Albion | 25 | 2 | 9 | 14 | 21 | 39 | -18 | 15 |
| > League One Full Table | |||||||||
