Bristol have suspended director of rugby Andy Robinson pending a "review of their coaching needs", and placed coach Mark Tainton in interim charge.
Robinson led the club back to the Premiership in May, ending their seven-year stay in the Championship.
But Bristol have lost all seven top-flight games so far this season, leaving them bottom of the table.
The 52-year-old former England and Scotland head coach has been in charge at Bristol since 2013.
Robinson only signed a new three-year contract with the Ashton Gate side in August, but they have since lost all nine of their competitive fixtures - including two in the European Challenge Cup.
A club statement said: "Bristol Rugby have decided, following the extremely disappointing start to the season, to appoint Mark Tainton as acting head coach with immediate effect."
Kicking coach Tainton, who joined Bristol prior to the start of the season, has previously worked at London Irish, Wasps and for the Ireland national team coaching staff.
"This is clearly a very difficult time for the club, but we remain confident we can retain our position in the Premiership," added Bristol chairman Chris Booy.
What has gone wrong at Bristol?
Since Bristol's long-awaited return to the top flight began with an encouraging 21-19 loss to Harlequins at Twickenham on the opening day, both results and performances have failed to meet expectations.
A heavy 70-22 defeat at Wasps on 18 September set the tone for a defence which has conceded 34 tries in seven league games.
Injuries have undoubtedly hampered Robinson's side, with 15 senior players ruled out of October's Challenge Cup loss at local rivals Bath.
Long-term absentees have included influential former Wales centre Gavin Henson, who was forced off injured in both of his two appearances this season, including Sunday's 31-13 home defeat by Sale Sharks.
BBC Radio 5 live rugby union reporter Chris Jones
"Bristol spent seven seasons down in the Championship, so it's no surprise that they have acted swiftly following their chastening start to their Premiership campaign.
"Although the club say Robinson is suspended, not sacked, it's hard to see him returning to take charge of team affairs, and it's likely the suspension is a case of negotiating severance.
"Mark Tainton will be acting head coach while a review is carried out, with Bristol needing a dramatic upturn in their fortunes on the pitch to avoid an immediate return to the second tier."