Larrechea suffered a suspected broken ankle during Sharks' 28-27 EDF Energy Cup victory over Harlequins, handing rugby director Philippe Saint-Andre potential problems for November league appointments with Wasps, Bristol, Newcastle and Quins.
"It could be a fracture," said Saint-Andre.
"He (Larrechcea) was very tough to play on, but it looked a bad injury to the bone. He could be out for six or seven weeks."
Larrechea's injury overshadowed a hard-fought win at the Twickenham Stoop that means Sale now face a Pool C decider against Llanelli Scarlets in early December.
"When you change nine or 10 players, it is difficult and the defence was sometimes shaky, but I am pleased with the character of my team," added Saint-Andre.
Quins, in contrast, have lost six successive league and cup games since returning to top-flight English rugby, which does not bode well for next Sunday's encounter with Premiership leaders Bristol.
Leicester booked their place in the Millennium Stadium semi-finals by beating Worcester 35-20. Tigers' second successive bonus point triumph meant they wrapped up Pool D with one round of group fixtures still remaining.
Centre Ollie Smith was the star of a five-try display at Sixways, showing signs that a summer's training with Australian rugby league giants Brisbane Broncos is starting to reap rewards.
"Ollie is coming back to form, " said Tigers head coach Pat Howard. "He has got genuine pace, and the way he created the first try was very good.
"He is a genuine threat, and I certainly would not like to mark him. He is not in the England picture at the moment, but he's progressing pretty well."
An international recall could be on the cards for 33-year-old Colin Charvis after he produced a towering performance in Newport Gwent Dragons' 26-7 win against Rodney Parade visitors Northampton.
Ex-Wales captain Charvis, who was snapped up by the Dragons after Newcastle released him earlier this year, played a key role in thwarting Saints' bid for a victory that might have kept Pool D alive.
"Colin is like most very good international players in that he does not make a lot of mistakes," said Dragons head coach Paul Turner.
"He did a few things that kept us in the game at certain times."