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 | Wycombe WanderersWycombe | 20 | 13 | 5 | 2 | 43 | 22 | 21 | 44 |
| 2 | Birmingham CityBirmingham | 18 | 13 | 3 | 2 | 34 | 16 | 18 | 42 |
| 3 | Wrexham | 21 | 12 | 6 | 3 | 31 | 14 | 17 | 42 |
| 4 | Huddersfield TownHuddersfield | 20 | 12 | 3 | 5 | 34 | 18 | 16 | 39 |
| 5 | Stockport CountyStockport | 21 | 10 | 6 | 5 | 34 | 22 | 12 | 36 |
| 6 | Lincoln CityLincoln | 21 | 8 | 7 | 6 | 28 | 25 | 3 | 31 |
| 7 | Reading | 20 | 9 | 4 | 7 | 30 | 30 | 0 | 31 |
| 8 | Bolton WanderersBolton | 19 | 9 | 4 | 6 | 28 | 29 | -1 | 31 |
| 9 | Barnsley | 21 | 8 | 6 | 7 | 29 | 30 | -1 | 30 |
| 10 | Mansfield TownMansfield | 19 | 8 | 4 | 7 | 23 | 22 | 1 | 28 |
| 11 | Charlton AthleticCharlton | 20 | 7 | 6 | 7 | 23 | 19 | 4 | 27 |
| 12 | Blackpool | 20 | 7 | 6 | 7 | 29 | 31 | -2 | 27 |
| 13 | Exeter CityExeter | 20 | 8 | 3 | 9 | 19 | 22 | -3 | 27 |
| 14 | Stevenage | 19 | 7 | 5 | 7 | 15 | 17 | -2 | 26 |
| 15 | Leyton Orient | 20 | 7 | 4 | 9 | 23 | 20 | 3 | 25 |
| 16 | Peterborough UnitedPeterborough | 20 | 7 | 3 | 10 | 38 | 37 | 1 | 24 |
| 17 | Wigan AthleticWigan | 20 | 6 | 6 | 8 | 19 | 18 | 1 | 24 |
| 18 | Rotherham UnitedRotherham | 19 | 6 | 5 | 8 | 19 | 21 | -2 | 23 |
| 19 | Bristol Rovers | 20 | 6 | 4 | 10 | 18 | 29 | -11 | 22 |
| 20 | Northampton TownNorthampton | 21 | 5 | 6 | 10 | 21 | 34 | -13 | 21 |
| 21 | Crawley TownCrawley | 19 | 5 | 4 | 10 | 20 | 32 | -12 | 19 |
| 22 | Cambridge UnitedCambridge | 20 | 4 | 5 | 11 | 20 | 35 | -15 | 17 |
| 23 | Burton Albion | 20 | 2 | 6 | 12 | 17 | 32 | -15 | 12 |
| 24 | Shrewsbury TownShrewsbury | 20 | 3 | 3 | 14 | 21 | 41 | -20 | 12 |
| > League One Full Table | |||||||||
