The struggling champions, whose season has been ravaged by a catalogue of injuries, have lost their last three Guinness Premiership games and have slipped 13 points off the play-off places.
But there was good news for Sale this week with captain Mark Cueto and versatile forward Chris Jones both released for club duty by England while fly-half Daniel Larrechea returns from suspension.
Laharrague was signed on loan from Perpignan for the rest of the season and his inclusion at full-back means Cueto, Sale captain in the absence of Jason Robinson, returns to the wing.
"It's tough at the moment and whilst we have lost our last three games against Wasps, London Irish and Saracens, we have not been slaughtered and I expect us to finish the season strongly," said Jones.
"Friday evening's game is a must-win game for us."
Worcester are bottom of the table and fighting for their Premiership lives but Jones insisted: "We will need to respect them as they arrive here on the back of a win against Bath last week.
"Worcester are dangerous when they play away from Sixways and have won four of their last six away games in all competitions. It should be a great game."
That victory over Bath hauled Worcester to within four points of Northampton but it came at a price and they travel north without Pat Sanderson, who broke a bone in his hand.
Scrum-half Matt Powell takes over as skipper while Tom Harding comes into the back row.
Saracens hope to maintain their title play-off push by defeating Newcastle at Kingston Park, especially as the Falcons are without England trio Jonny Wilkinson, Mathew Tait and Toby Flood, plus injured full-back Matt Burke.
Saracens rugby director Alan Gaffney has brought David Seymour, Hugh Vyvyan, Paul Gustard, Tom Ryder and Alan Dickens back into the side.
Thomas Castaignede returns from a hamstring injury to take a place on a replacements bench.
"We played some good rugby against Sale last week. We played with ambition despite the conditions and we were also able to close out the game," said Gaffney.
"We have got six games remaining in the Premiership, and all of them are vital if we are going to maintain our push for a top four spot."
On Saturday, Premiership leaders Leicester head to Gloucester while second-placed Bristol will look to close the gap with a victory over London Irish, who have lost both Mike Catt and Shane Geraghty to international duty.
The Stoop is sold out for the first time this season for the visit of Wasps, who have lost 12 players to international action.