"It has become obvious to us during our training week that Gareth isn't going to be fit in time to be available for the first Test on tour and so we have taken the difficult decision to leave him at home and bring in cover in that specialist position," said Wales coach Robin McBryde.
"It's a tough call for Gareth, but he has had a glimpse of what is possible now and he knows he will get the rewards again in the future if he retains the same high standards he has shown us already.
"Daniel has a real opportunity to make an impact and we expect him to pick things up as quickly as possible and get stuck straight into training tomorrow morning."
The 21-year-old Evans is a former Wales U20s international who featured in the same age group side as the likes of Wales colleagues Dan Biggar, Josh Turnbull and British Lions tourist Leigh Halfpenny.
He has played six times for the Scarlets this season and is primarily a full-back although he has also turned out at fly-half in the Principality Premiership for Llanelli