To add to their woes top-scorer Karl Hawley limped off in the 22nd minute, with an ankle injury.
Chesterfield were satisfied with a point to ease their relegation worries from a game that only came to life in the second half.
Before the break neither keeper was troubled.
Paul Thirlwell made a vital eighth minute tackle to snuff out Peter Holmes' shooting chance when the Chesterfield man forced his way into the box and hardworking Spireites midfielder Derek Niven fired a 25-yard piledriver over the UNited bar.
It was 19 minutes before Carlisle posed any sort of threat - Hawley just unable to cash in on a wild Mark Allott back-pass that flew just past him.
And Carlisle had to re-shuffle after 22 minutes when the 12-goal striker limped off.
Luke Joyce replaced him, slotting into midfield with raw American teenager Johann Smith pushing up to partner 18-year-old Joe Garner up front.
Another long-range rocket from Niven flew narrowly over on the half-hour before Colin Larkin came close to breaking the deadlock.
Carlisle failed to clear a corner and Larkin's snap-shot from the corner of the six-yard box was deflected over the bar by Danny Livesey.
At the other end, Livesey met a free kick from Zigor Aranalde with a glancing header just wide of the post before Chesterfield survived a self-inflicted scare.
Jeff Smith - easily Carlisle's best man - lofted a free-kick into Chesterfield's crowded box and Niven crashed a header against his own bar before the ball was scrambled clear.
The first on-target shot came a minute into the second half, but Alex Bailey's shot was too weak to worry keeper Keiren Westwood.
Then Spireites keeper Barry Roche brilliantly tipped a Peter Murphy header over the bar from a Jeff Smith corner.
Westwood was sharply down to his left to turn away a fizzing Holmes' drive one-handed, but Roche pulled off another fine save nine minutes from the end to deny Carlisle.
Garner's through ball over Chesterfield's defence sent Jeff Smith through on goal, but the keeper was smartly off his line to beat away his 15-yard drive.
And, with four minutes to go, Westwood tipped an angled 25-yarder from Wayne Allison over the bar one-handed.