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 | 11 | 9 | 1 | 1 | 21 | 6 | 15 | 28 |
| 2 | Manchester CityMan City | 11 | 7 | 2 | 2 | 22 | 13 | 9 | 23 |
| 3 | Chelsea | 11 | 5 | 4 | 2 | 21 | 13 | 8 | 19 |
| 4 | Arsenal | 11 | 5 | 4 | 2 | 18 | 12 | 6 | 19 |
| 5 | Nottingham ForestNott'm Forest | 11 | 5 | 4 | 2 | 15 | 10 | 5 | 19 |
| 6 | Brighton & Hove AlbionBrighton | 11 | 5 | 4 | 2 | 19 | 15 | 4 | 19 |
| 7 | Fulham | 11 | 5 | 3 | 3 | 16 | 13 | 3 | 18 |
| 8 | Newcastle UnitedNewcastle | 11 | 5 | 3 | 3 | 13 | 11 | 2 | 18 |
| 9 | Aston Villa | 11 | 5 | 3 | 3 | 17 | 17 | 0 | 18 |
| 10 | Tottenham HotspurSpurs | 11 | 5 | 1 | 5 | 23 | 13 | 10 | 16 |
| 11 | Brentford | 11 | 5 | 1 | 5 | 22 | 22 | 0 | 16 |
| 12 | Bournemouth | 11 | 4 | 3 | 4 | 15 | 15 | 0 | 15 |
| 13 | Manchester UnitedMan Utd | 11 | 4 | 3 | 4 | 12 | 12 | 0 | 15 |
| 14 | West Ham UnitedWest Ham | 11 | 3 | 3 | 5 | 13 | 19 | -6 | 12 |
| 15 | Leicester CityLeicester | 11 | 2 | 4 | 5 | 14 | 21 | -7 | 10 |
| 16 | Everton | 11 | 2 | 4 | 5 | 10 | 17 | -7 | 10 |
| 17 | Ipswich TownIpswich | 11 | 1 | 5 | 5 | 12 | 22 | -10 | 8 |
| 18 | Crystal Palace | 11 | 1 | 4 | 6 | 8 | 15 | -7 | 7 |
| 19 | Wolverhampton WanderersWolves | 11 | 1 | 3 | 7 | 16 | 27 | -11 | 6 |
| 20 | Southampton | 11 | 1 | 1 | 9 | 7 | 21 | -14 | 4 |
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