Cobblers summer signing Giles Coke has undergone a hernia operation and will be out of action for a further three weeks.
Coke, who was signed from Mansfield Town over the summer in a deal worth 70,000, has yet to play for Northampton.
Coke was unfit when he signed on at Sixfields following a knee ligament injury sustained in January, and after working his way back to fitness he suffered what was thought to be a groin problem a fortnight ago.
But it was discovered that Coke had in fact suffered a hernia problem, and he went under the knife on Tuesday.
"Giles had a hernia problem so he went up to Manchester for a minor operation, which is a hernia repair," revealed Cobblers boss Stuart Gray.
"It means he is going to be out for three weeks, which is a major setback for him, and a disappointment for us and the team because he was getting very close to actually being involved with the first team.
"It is a setback but fingers-crossed this will be the last of his problems and we will see him before the new year."
The Cobblers entertain Carlisle United at Sixfields on Saturday, and apart from Coke and fellow long-term injury victim Chris Doig, Gray has a full squad to pick from.
Town go into the game on the back of five straight league defeats, a run that has also seen them fail to score a goal.
Don't miss Friday's Chronicle & Echo for full preview & stats of Saturday's big game