Laidlaw had been struggling with the problem for a fortnight and suffered another knock in a practice match on Tuesday.
"He felt a bit of discomfort - really a lack of power - so under thecircumstances he has stood down," said team manager Roy Laidlaw.
Iain Fairley, who has three full caps, has been drafted in as replacement.
Manager Laidlaw added: "Iain is one player who has been with the sevens squad in every tournament since we played as the NIG Scottish Thistles in Henley-on-Thames last year.
"He is a scrum-half as opposed to Clark operating at stand-off but we feel with both Mike Blair and Marcus Di Rollo in the squad we have midfield cover.
"Iain can also play in the centre so we still have versatility."
Scotland are in the same pool as Niue, Canada and favourites New Zealand.
Their first game is on Friday against Niue.