Michael O'Neill's already depleted squad are set to travel to South America later this month for tough friendlies against Uruguay and Chile, and saw Ward and Paterson withdraw their services earlier this week.
Cliftonville striker Boyce has been in prolific form since returning to his homeland from Werder Bremen in 2012, scoring 51 goals in 85 league appearances.
The 23-year-old has four senior caps to his name and will now be looking to add to that tally and stake a claim for a leading role in his country's UEFA Euro 2016 qualifying campaign.
Accrington Stanley's Gray will also be keen to make a big impression on his first call-up to the senior side, making the step up from the Under-21s.
O'Neill's travelling party will be without big names including Jonny Evans, Gareth McAuley, Chris Brunt and Kyle Lafferty for the double header.
