The 21-year-old forward moves to Elland Road from Paraguayan top-flight side Nacional.
Leeds said that they have the option to make Montenegro's move permanent at the end of the season if he is "successful".
Montenegro spent the 2011-12 season on loan at West Ham Untied in the Championship, but didn't make an impact with the Hammers.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Manchester CityMan City | 31 | 23 | 5 | 3 | 66 | 21 | 45 | 74 |
| 2 | Manchester UnitedMan Utd | 30 | 17 | 9 | 4 | 58 | 33 | 25 | 60 |
| 3 | Leicester CityLeicester | 30 | 17 | 5 | 8 | 53 | 34 | 19 | 56 |
| 4 | West Ham UnitedWest Ham | 30 | 15 | 7 | 8 | 48 | 37 | 11 | 52 |
| 5 | Chelsea | 30 | 14 | 9 | 7 | 46 | 30 | 16 | 51 |
| 6 | Tottenham HotspurSpurs | 30 | 14 | 7 | 9 | 51 | 32 | 19 | 49 |
| 7 | Liverpool | 30 | 14 | 7 | 9 | 51 | 36 | 15 | 49 |
| 8 | Everton | 29 | 14 | 5 | 10 | 41 | 38 | 3 | 47 |
| 9 | Aston Villa | 29 | 13 | 5 | 11 | 42 | 31 | 11 | 44 |
| 10 | Arsenal | 30 | 12 | 6 | 12 | 40 | 35 | 5 | 42 |
| 11 | Leeds UnitedLeeds | 30 | 13 | 3 | 14 | 47 | 48 | -1 | 42 |
| 12 | Wolverhampton WanderersWolves | 31 | 10 | 8 | 13 | 31 | 41 | -10 | 38 |
| 13 | Crystal Palace | 30 | 10 | 8 | 12 | 32 | 48 | -16 | 38 |
| 14 | Southampton | 30 | 10 | 6 | 14 | 39 | 53 | -14 | 36 |
| 15 | Burnley | 30 | 8 | 9 | 13 | 24 | 40 | -16 | 33 |
| 16 | Brighton & Hove AlbionBrighton | 30 | 7 | 11 | 12 | 33 | 38 | -5 | 32 |
| 17 | Newcastle UnitedNewcastle | 30 | 7 | 8 | 15 | 30 | 50 | -20 | 29 |
| 18 | Fulham | 32 | 5 | 11 | 16 | 24 | 42 | -18 | 26 |
| 19 | West Bromwich AlbionWest Brom | 30 | 4 | 9 | 17 | 25 | 59 | -34 | 21 |
| 20 | Sheffield UnitedSheff Utd | 30 | 4 | 2 | 24 | 17 | 52 | -35 | 14 |
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