But the 20-year-old is determined to change nothing about his game after being handed his big chance by head coach Frank Hadden, and will try to treat it like any other match.
Barclay and Alasdair Dickinson will win their first Scotland caps in the Pool C encounter, after Hadden made 13 personnel changes and two more positional alterations from the side which played against Romania on Tuesday.
Hadden has decided to rotate the squad in order to keep as many players as possible fresh during a run of three games in 11 days.
Most of Scotland's key players have been rested ahead of next Saturday's crunch match against Italy in St Etienne.
That game looks certain to decide who will progress from Pool C to the World Cup knock-out stages along with New Zealand.
"I just have to play the same game as I play for Glasgow," said Barclay.
"There's no point me going out there and trying to do something different which is not in my game just because it's the All Blacks."
The open-side flanker will celebrate his 21st birthday on Monday, but for now his focus is on rugby rather than parties.
He added: "Most of the conversations I've had with the other guys in the squad have been about me trying to get a few hints which will help me put aside my nerves.
"The main thing they have said is that it will all be over before I know it, so I have to go out there and enjoy the experience.
"As soon as my name was read out there was that feeling of ecstasy, but literally within seconds it turned to nerves.
"But I'm going to try not to be overawed by the situation. I can't help but think a lot about the game - especially as it is my first cap, against the tournament favourites and opposite the best player in my position in the world - but I can't let it get to me.
"The night I first found out I didn't sleep that well, I was dosing off then waking up thinking about it.
"That's not doing me any good so I'm trying to put it to the back of my mind and just concentrating on training, and almost letting the game come to me."