The 21-year-old spent part of last season at the Keepmoat Stadium, making 18 appearances for the club.
Johnstone has been loaned out to a number of teams in recent years, including Scunthorpe United, Walsall and Yeovil Town.
Doncaster are back in action on Saturday when they travel to Bradford City in League One.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Liverpool | 23 | 17 | 5 | 1 | 56 | 21 | 35 | 56 |
| 2 | Arsenal | 24 | 14 | 8 | 2 | 49 | 22 | 27 | 50 |
| 3 | Nottingham ForestNott'm Forest | 24 | 14 | 5 | 5 | 40 | 27 | 13 | 47 |
| 4 | Chelsea | 24 | 12 | 7 | 5 | 47 | 31 | 16 | 43 |
| 5 | Manchester CityMan City | 24 | 12 | 5 | 7 | 48 | 35 | 13 | 41 |
| 6 | Newcastle UnitedNewcastle | 24 | 12 | 5 | 7 | 42 | 29 | 13 | 41 |
| 7 | Bournemouth | 24 | 11 | 7 | 6 | 41 | 28 | 13 | 40 |
| 8 | Aston Villa | 24 | 10 | 7 | 7 | 34 | 37 | -3 | 37 |
| 9 | Fulham | 24 | 9 | 9 | 6 | 36 | 32 | 4 | 36 |
| 10 | Brighton & Hove AlbionBrighton | 24 | 8 | 10 | 6 | 35 | 38 | -3 | 34 |
| 11 | Brentford | 24 | 9 | 4 | 11 | 42 | 42 | 0 | 31 |
| 12 | Crystal Palace | 24 | 7 | 9 | 8 | 28 | 30 | -2 | 30 |
| 13 | Manchester UnitedMan Utd | 24 | 8 | 5 | 11 | 28 | 34 | -6 | 29 |
| 14 | Tottenham HotspurSpurs | 24 | 8 | 3 | 13 | 48 | 37 | 11 | 27 |
| 15 | West Ham UnitedWest Ham | 24 | 7 | 6 | 11 | 29 | 46 | -17 | 27 |
| 16 | Everton | 23 | 6 | 8 | 9 | 23 | 28 | -5 | 26 |
| 17 | Wolverhampton WanderersWolves | 24 | 5 | 4 | 15 | 34 | 52 | -18 | 19 |
| 18 | Leicester CityLeicester | 24 | 4 | 5 | 15 | 25 | 53 | -28 | 17 |
| 19 | Ipswich TownIpswich | 24 | 3 | 7 | 14 | 22 | 49 | -27 | 16 |
| 20 | Southampton | 24 | 2 | 3 | 19 | 18 | 54 | -36 | 9 |
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