Derry limped out of the action 11 minutes from time with what was first thought to be cramp, but the former Crystal Palace play-off winner had an inconclusive scan on the problem over the weekend and is rated doubtful.
If Derry misses out, Blackwell will be forced into a major re-shuffle of the Leeds engine room.
The Leeds boss has no other new injury worries, although Richard Cresswell will again play through the pain barrier if he is involved against his former club.
Preston, who are unbeaten in 18 matches at Deepdale, will name an unchanged squad.
Leeds squad: Sullivan, Kelly, Gregan, Kilgallon, Crainey, Miller, Bakke, Stone, Douglas, Derry, Healy, Hulse, Lewis, Blake, Bennett, Cresswell, Beckford, Richardson, Moore, Pugh, Walton, Harding, Griffiths.