If Newcastle lose then runners-up berth is the best they can realistically hope for.
Recent history is not in the Falcons' favour, given a 41-12 defeat against Brive last season, which remains their heaviest Challenge Cup loss.
But Fletcher said: "I feel as if the squad has moved forward massively from where we were when we played out in Brive last season.
"I am expecting a much higher standard of performance.
"We go into this game on the back of two Guinness Premiership wins, but we know we have to lift our levels from last weekend when we were forced to grind it out against Worcester.
"They (Worcester) came to Kingston Park with a very specific game plan to kill our ball - I know that because they left their match notes in the changing room after the game - and we know Brive will be another big test in the forwards."
The Falcons welcome back former All Blacks prop Joe McDonnell, but England centre Jamie Noon has remained in Newcastle while his daughter Elodie recovers from an accident.
Fletcher added: "Brive are a team that plays off momentum.
"When you are in France and the brass band starts playing, the crowd get their gander up and the noise level increases, that sort of atmosphere inspires these guys and fires them up massively.
"That asks certain questions of our players, but then that is what sport is all about, and I expect us to be able to respond to the challenge."
Sale Sharks and Worcester will both confirm quarter-final places if they beat respective opponents Petrarca and Montauban on Friday night.
Sale, having amassed a maximum 20 points from four games to head Pool Four, should secure another bonus point win at Edgeley Park, while Pool Two leaders Worcester will be in France aiming to preserve their 100% record.
Richard Wigglesworth, one of three scrum-halves in England's RBS 6 Nations squad, is handed a rare start in the Sale number 10 shirt, while Worcester include New Zealand imports Rico Gear and Sam Tuitupou.
Leeds Carnegie host Pool Five opponents Dax, needing victory to remain in pole position ahead of a possible group decider against Castres next Thursday.
And Saturday's action includes a trip to Italy for Pool One leaders Bath, who can celebrate head coach Steve Meehan agreeing a new two-year contract by defeating Overmach Parma and booking a quarter-final place.