Howarth will be in plaster for the next three weeks
Carlisle United are facing a mounting injury list as they battle to avoid relegation from League One.
The Cumbrians currently have nine first-team players out of action with goalkeeper Chris Howarth and defender Ian Harte the latest casualties.
Howarth fractured his fibula during a reserve-team game and has been ruled out for the rest of the season.
Harte broke his hand at the weekend and may also be out for the season, although he could continue playing.
The Cumbrians currently lie 19th in League One, just one point above the relegation places.
Howarth picked up the injury during the 1-1 draw with Preston's reserves on Monday, while new signing Harte picked up his injury 10 minutes into the second half of Saturday's 1-1 draw with Northampton.
Former Leeds defender Harte, 31, will be out for at least three games after it was discovered he had fractured two metacarpals during the game.
The Republic of Ireland international will now receive a full cast on the affected area and will be reassessed in a fortnight's time.
He joins Danny Livesey, Peter Murphy, Marc Bridge-Wilkinson, Paul Thirwell, Michael Burns, Kevin Gall and Gary Madine on the sidelines.
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