McNicholl had stood out for Glenn Delaney’s men on the Cote d’Azur last Saturday night, but he went down in the final few minutes and had to limp away from the action.
The Scarlets have now confirmed he will be unavailable for the next eight weeks which means he is unlikely to feature in the new Autumn Nations Cup tournament.
He will also miss the start of the 2020/21 Guinness PRO14 season
McNicholl, 30, is equally comfortable at wing or full-back.
He made his first Wales appearance in the non-capped game with the Barbarians in November 2019 and scored a try.
He has since gone on to win four Test caps, all of which came in the Six Nations at the start of the year.
McNicholl’s Scarlets and Wales team-mate Leigh Halfpenny is back in full training after leaving the field in the 11-6 loss to Toulon for a head injury assessment.
Halfpenny has since completed all the return to play protocols.
The Scarlets have also confirmed wing Tomi Lewis will unfortunately be out of action for the next 12 months after undergoing knee surgery on a serious injury suffered in training.
