He will get his third outing of the tour against the Waratahs in Sydney on Saturday, but doesn't believe that he is now the favourite to pack down in the Test side just because he is the last one of the original picks in his position.
"Definitely not. The coaches wouldn't have brought out Alex and Ryan if they didn't think they were good enough to play in the Test series. I've just got to keep my head down and keep working hard," said Vunipola.
"Every player wants to play in the Tests. I knew with Gethin Jenkins and Cian Healy here, two solid Test props, that I'd have my work cut out - I knew I would have to work hard to push for the Test team. It's been going well so far and hopefully I can keep it going.
"To get three games in a row is great and I've had more chances than most players. Personally, the coaches seem happy with what I am doing so far, although obviously there is still room to improve and I need a good performance on Saturday.
"Every chance you get to pull on the red Lions jersey is a chance to push for the Test side. This game is no different - I'll just go out there and play the same game."
The 20st 7lb front row giant has caught the eye with his blockbusting runs so far on tour and he bagged his first try against the Western Force in Perth. But he has also been working hard on his scrimmaging with forwards coach Graham Rowntree and is developing more to his game than banging up the middle.
"I've been working with Graham and he has been helpful here, and with England. The same set-up has been helpful for me and Graham has been a mentor for me since 18 and helped me a lot," said Vunipola.
"Being out here with so many class players you can't help but learn off them. Having Alex and Ryan come out has heightened the competition, although there is a lot of competition in all positions.
"It has certainly helped having Corbs here because I know him from the England camp and he is someone I get on well with. Ryan, too is my room mate at the moment, so that is good as well.
"I've seen a few of the Waratahs' games and they did well against the Western Force after they had played us. They looked quite strong - a lot stronger than the Force and probably than the Reds. They will be strong up front and we know we will have our work cut out."