Centre-back McClelland, 19, has played for the Northern Ireland U17s and U19s.
Steven Davis and Jonny Evans are among the experienced players rested.
Corry Evans, Conor McLaughlin, Jamal Lewis, Michael Smith, Michael McGovern and Trevor Carson will also not be involved in the behind-closed-doors match against Malta in Austria, which has been brought forward from Monday to Sunday, and next Thursday's game in Ukraine.
Manager Ian Baraclough said the inclusions of McClelland and Bradley were part of his "fast-tracking" plans.
"Conor's had a really good season with Liverpool - his first year there - he's played regularly in the U23s and was in the FA Youth Cup final the other night," added the Northern Ireland boss.
"We just feel his development has been has been very, very good this season. And to give him the knowledge of what it's like with this group, we thought it was the right time.
"With Jonny [Evans] not here and Dan Ballard involved with the play-off final with Blackpool as a centre-half, we felt it was the right time to bring Sam through. And again, let's see what is what is what he's about as an individual."
Northern Ireland squad:
Defenders: Cathcart (Watford), Dallas (Leeds United), Ferguson (Millwall), McNair (Middlesbrough), Ballard (Arsenal - on loan at Blackpool), Brown (Cardiff City), McClelland (Chelsea), Bradley (Liverpool)