Gray blow for Scotland
Toulouse lock Gray has been battling a back injury and illness, while Hidalgo-Clyne – called up to replace British and Irish Lions scrumhalf Greig Laidlaw – has torn his hamstring.
Hidalgo-Clyne's uncapped Edinburgh teammate, Sean Kennedy, has been brought in to take his place, but no replacement was announced for Gray.
"Richie has been unable to do much training since the RBS 6 Nations because of his back issues, so it became quickly evident he wouldn't be able to play Test-match rugby," said coach Gregor Townsend in a statement on the Scottish Rugby website.
"We're all disappointed for Sam, who came into camp full of enthusiasm and worked really hard in our first three days together.
"While it's a blow for him to miss the tour, at least his injury isn't too serious and he can get back into pre-season with Edinburgh at a later date.
"It's great that we have been able to call up a quality replacement in Sean Kennedy and we look forward to working with him over the next couple of weeks."
Scotland will play Italy in Singapore on June 10, followed by Australia in Sydney on June 17 and Fiji in Suva on June 24.
