Western Force captain Michael Wells says his team's mindset will be the determining factor on whether they beat the ladder-leading Chiefs and gatecrash the Super Rugby Pacific finals.

The Force's finals fate is no longer in their own hands following last week's embarrassing 52-14 loss to the Melbourne Rebels.

The result dropped the Force to ninth spot, one point adrift of the Highlanders and two points behind the Queensland Reds.

It means the Force must defeat the Chiefs on Saturday night in Perth - and hope at least one of the Highlanders or Reds lose - in order to sneak into the crucial top eight.

"We're here to play finals. You don't need any more motivation than that," Wells told reporters on Tuesday.

"There is no tomorrow after this game if we don't get the result."

The Force have suffered a number of big losses this year.

There was the 71-20 battering by the Reds in round two, the 36-16 defeat to the Waratahs in round seven, and last week's 38-point loss to the Rebels.

Wells believes his team's problems have stemmed from a poor approach at key moments, rather than a lack of ability.

"Mindset, not skillset," Wells replied when asked about the message leading into Saturday's must-win clash with the Chiefs.

"When we've seen the really bad performances - we look at last week, we look at the Reds game - it's a mindset (thing).

"We haven't shown up and done our job. We've gone away, we've gone individual.

"Usually the war of the game is a mindset battle. If you want to run over the top of someone, you generally will.

"If you want to tackle someone and knock them back more than they want to run over you, you generally will.

"It's getting the mindset right, because we know the skillset is there."

The Chiefs (12-1) are guaranteed to finish top, meaning they may send a second-string squad across to Perth in order to rest their stars ahead of the finals.

Wells said no matter who the Chiefs put on the field, Saturday's clash will be a tough task.

"Whether they send the guys who are internationals, or whether they send the guys who are strong squad members, whatever they roll out we're going to have to match," Wells said.