The 28-year-old former Derby County keeper, who played 22 times for City earlier this season, suffered ligament damage in an under-21 match on Monday.
As a result, teenager Max O'Leary has been recalled from his loan spell at non-league Kidderminster Harriers.
"I feel really sorry for him (Fielding)," head coach Lee Johnson told the club website.
"He's gone from being an ever-present in last year's success to his injury troubles which have thwarted his season this time around."
Bristol City goalkeeper Frank Fielding will miss the rest of the season after being sidelined with an ankle injury.