TOWN have a big doubt over Nathan Clarke for Saturday's important clash with bottom club Carlisle at the McAlpine.
The 19-year-old defender took a knock on an ankle in Tuesday's 2-1 defeat at Yeovil which was okay at the time but has since stiffened up badly.
Clarke - who watched his 15-year-old brother Tom play in last night's FA Youth Cup victory against Grimsby - did not train yesterday and was again missing from the first-team session today.
The news comes just 24 hours before striker Jon Newby sees a specialist about a knee injury and puts a big question mark over Clarke's availability against Carlisle, who have Chris Billy in their ranks and whose assistant manager is one-time Town coach Dennis Booth.
"Clarkey got the injury in the first-half at Yeovil and his boot came off in the tackle, but he was able to carry on and it's only since then the ankle has become really swollen," said Jackson today.
"He is having further treatment today and we'll have to take a look at him tomorrow to see if he has any chance of making the game.
"With Jon Newby, he's been niggled by this knee complaint for about 10 days and hasn't fully recovered, so we need to see if there's any damage in there which needs to be sorted out."
Jackson has Paul Scott and teenager David Mirfin waiting in the wings for a chance as Town aim to bounce back from successive away defeats.
"We lost our shape and discipline at Lincoln to lose the game and I was bitterly disappointed at Yeovil, because it was a game we should have won.
"Once again, though, we lost it at the back once they went in front and our passing was appalling, so while Yeovil were saying we were the best team they've played all season, I'd have to disagree.
"We have to put things right on Saturday in what is a no-win game for us. If we take three points it's expected and if we lose, it's a crisis.
"I told the players yesterday, I will tell them today and I'll remind them tomorrow and Saturday that we can't take this Carlisle game lightly.
"Carlisle will be fighting for their lives, they will want to do well here at the McAlpine and we need a performance like we've been giving at home."
Town fans are reminded it's all-ticket for the match at Scunthorpe on Saturday week and these are on sale at the McAlpine priced £14 for adults and £8 concessions (seats are behind the goal).