The 18-year-old defender has moved to the League One side following Elliott Hewitt's return to Ipswich Town.
Hammers academy product Harney has represented Northern Ireland at Under-21 level.
Colchester are back in action on Friday when they travel to Barnsley in the league.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Liverpool | 12 | 10 | 1 | 1 | 24 | 8 | 16 | 31 |
| 2 | Manchester CityMan City | 12 | 7 | 2 | 3 | 22 | 17 | 5 | 23 |
| 3 | Chelsea | 12 | 6 | 4 | 2 | 23 | 14 | 9 | 22 |
| 4 | Arsenal | 12 | 6 | 4 | 2 | 21 | 12 | 9 | 22 |
| 5 | Brighton & Hove AlbionBrighton | 12 | 6 | 4 | 2 | 21 | 16 | 5 | 22 |
| 6 | Tottenham HotspurSpurs | 12 | 6 | 1 | 5 | 27 | 13 | 14 | 19 |
| 7 | Nottingham ForestNott'm Forest | 12 | 5 | 4 | 3 | 15 | 13 | 2 | 19 |
| 8 | Aston Villa | 12 | 5 | 4 | 3 | 19 | 19 | 0 | 19 |
| 9 | Fulham | 12 | 5 | 3 | 4 | 17 | 17 | 0 | 18 |
| 10 | Newcastle UnitedNewcastle | 12 | 5 | 3 | 4 | 13 | 13 | 0 | 18 |
| 11 | Brentford | 12 | 5 | 2 | 5 | 22 | 22 | 0 | 17 |
| 12 | Manchester UnitedMan Utd | 12 | 4 | 4 | 4 | 13 | 13 | 0 | 16 |
| 13 | Bournemouth | 12 | 4 | 3 | 5 | 16 | 17 | -1 | 15 |
| 14 | West Ham UnitedWest Ham | 12 | 4 | 3 | 5 | 15 | 19 | -4 | 15 |
| 15 | Everton | 12 | 2 | 5 | 5 | 10 | 17 | -7 | 11 |
| 16 | Leicester CityLeicester | 12 | 2 | 4 | 6 | 15 | 23 | -8 | 10 |
| 17 | Wolverhampton WanderersWolves | 12 | 2 | 3 | 7 | 20 | 28 | -8 | 9 |
| 18 | Ipswich TownIpswich | 12 | 1 | 6 | 5 | 13 | 23 | -10 | 9 |
| 19 | Crystal Palace | 12 | 1 | 5 | 6 | 10 | 17 | -7 | 8 |
| 20 | Southampton | 12 | 1 | 1 | 10 | 9 | 24 | -15 | 4 |
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