Wayne Rooney believes his game has changed for the better amid questions over his inclusion in England's starting side.

England opens its UEFA EURO 2016 campaign against Russia in Marseille on Sunday (AEST) having claimed three wins from three in pre-tournament warm-ups.

Captain Rooney started in England's final friendly against Portugal in an attacking trio with Harry Kane and Jamie Vardy.

However, England struggled to break down 10-man Portugal before Chris Smalling's 86th-minute header clinched victory.

With Rooney scoring just eight Premier League goals this season, his place in the side has come under scrutiny but the 30-year-old - who has adapted to a role in midfield for Manchester United in recent times - still has great confidence in his abilities.

"I think everyone who watches the game is entitled to their opinions, I know the qualities I have and I don't think I have to sit here and defend myself," Rooney said.

"I have played this game for a lot of years and I am aware my game has changed over years, in my opinion for the better.

"I changed my game slightly. I've seen players do that over years, who have played in a different way to what they did and became better players, it's natural for a footballer.

"Over last few months at Man U I've played midfield, it's a natural way of football, it happens. I always feel with my football intelligence I can play there and further my career there as well."

"There is a real buzz around the place and everyone is excited, it is important performance levels match.

"We've got a talented squad capable of big things, but tournament football is different. It will be a challenge for us as a squad but we're confident we can do well."