Croft takes his place in the back row for Johnson’s first game as England team manager after starting the season with a series of impressive displays for Leicester Tigers.
The 22-year-old says he still has plenty to work on as he aims to secure his place in the England side.
Croft, who is set to win his fifth international cap, said: “I've been happy with the way things have gone at the start of the season.
“There are a number of things I need to work on but I'm grateful that Johno has given me the nod and I'll just try to work as hard as I can to secure that place.”
The game against the Pacific Islanders kicks off the autumn internationals which will see England also take on Australia, world champions South Africa and New Zealand at Twickenham.
Croft warned England are in for a physical encounter on Saturday and stressed the need for concentration.
He said: “It's a massive game. They are a very physical and skilled team and it's going to be tough. A lot of the players are in the Premiership along with us.
“It's the first of four huge games but we can't look too far into the future otherwise we will trip up in the present. We are thoroughly concentrating on the first game to make sure our drills are right, our scrums and line-outs, and hopefully we can get to Twickenham and play some positive rugby.”
The Tigers Academy graduate added: “The summer tour seems a long time ago with all the domestic competitions but we have got our England heads back on now and we are looking forward to the first game.
“With the new EPS agreement we are here two weeks before our first match and it means we get to know each other again and get the moves as sorted.”
His Welford Road teammate Toby Flood, meanwhile, aims to fight his way back into Johnson’s starting line-up after being named on the bench alongside Tigers scrum-half Harry Ellis.
Flood, who has won 18 caps, said: “I'm keen to fight my way back into the starting line-up. I was disappointed to be left out but there are four games ahead and competition for places can only be a good thing.
“Training has been really good, I’m loving the fresh new atmosphere, there's a great feeling in the camp. Everyone is very excited.”