Fiji coach Inoke Male said England, France, Australia and New Zealand are "vultures" who send scouts to school championships in the region to pick off the best youngsters.
Yet in the below Q&A with Eurosport, New Zealand-born Vunipola, several of whose family have represented Tonga, denies that this is the case.
He also looks ahead to the possibility of making his debut in the first of four autumn internationals at HQ which also see England take on Australia, South Africa and New Zealand.
Can you tell those fans who haven't yet seen you in action about yourself as a player?
I'm a prop but I like to get all over the place as well with the ball in hand. I like to think I work hard for the team.
You break the gain line a fair bit for a 20-stone forward...
I wouldn't say I've got a turn of pace though - I'm good at a lot of things but not exceptional at anything!
How have you found playing in the Premiership?
After stepping up from the Championship it was tough last year but we're second in the table at the moment and I'm really enjoying it. Personally I'm really happy with how I've performed so far this season.
What are the main differences between the divisions? Is it a more physical game for you now?
Definitely - there's more physicality and the speed of the game as well. Every player is a good player and every team is a good team so you never go into a game thinking 'this will be a walkover'. It's also a long season as well so the body's got to get used to that, and it's tougher mentally.
You've made changes to your lifestyle away from the pitch. How has that helped?
It's definitely made a difference. To get to a high level you obviously have to look after yourself in more ways than one - you have to be good at training but outside that you have to focus on the nutritional stuff and be a bit more smart. Every time I eat something I have to think 'is this the right thing to do?' It helps you to train and play better - you can see the results on the pitch.
You've come a long way in a short time - how are you feeling about it all?
I don't think too much about it. I just keep working hard and focus on my training.
You've played with the younger England sides, but are you surprised at the speed with which you have been called up?
Very surprised. There's a lot of good props out there at the moment - young props as well - so I was very surprised to get a shout. But I can't just be happy with being here - I have to push on and show the coaches what I can do.
How many of the guys in the squad do you know?
I know a few - a few from the youth teams and a few from Sarries as well. All the guys are top guys as well so it's been easy to settle in.
There's talk that you will come on on Saturday. Have you been told whether you will play?
No, I haven't heard anything, just the talk like you have. I've just got to keep my head down and work hard in training. The team is announced on Thursday so we'll see.
What will it feel like to run out at Twickenham?
I can't be thinking about that! I've got to impress the coaches enough to be involved and see what happens. I'd love to play against Fiji [though]... if I do, I have to think about my set-piece.
What made you choose to represent England?
When I was growing up it was always England. When I moved over to the UK I lived in Wales but I always wanted to play for England. They are one of the top sides in the world and if you want to play top rugby, you have to play in the best teams.
You're from a rugby background. Can you tell us about it?
My dad's family all played for Tonga - my grandad and all my uncles; 1999 was the last time a family member played for them. Then we moved over here when I was young so my dad could play rugby at Pontypool.
What positions did they play, and what effect have they had on your career?
A bit of a mix of backs and forwards. My dad got me into training, doing push-ups and running and stuff. Because of them I started playing the game at a young age and just enjoyed it.
Fiji coach Inoke Male spoke recently about big rugby nations poaching youngsters from the Pacific Islands. What did you make of what he said?
As an Islander you have to go abroad looking for opportunities and if you work hard to play for that country, you deserve your chance. There's no poaching going on or anything like that. I can't decide what he thinks, but if you want to [play for an adopted country], then it's fair enough.
Mako Vunipola was speaking at the launch of O2 Inside Line, the weekly behind the scenes show from inside the England camp. For the latest episode and to receive email alerts for each show, visit