Eddie Jones has warned world rugby it faces imminent dangers from the growing big beast problem - as well as the threat his Japan side are posing to the game's big boys.

Japan pulled off the biggest shock in World Cup history by beating two-time winners South Africa 34-32 at the weekend, and are looking to take another scalp against Scotland in Gloucester on Wednesday.

Japan head coach Eddie Jones faces the media© Mike Hewitt/Getty Images

"I think rugby is going in a dangerous direction; players are getting bigger and stronger and faster and the field is staying the same size," Jones said before Japan left Brighton.

"Defensively, you have 14 or 15 players on their feet, where in days gone by there would be two or three laying on the ground. Something needs to be done to make it more fatiguing. The problem is the power is there the whole game.

"You have 15 players and you can replace half your team. You replace one guy with 125 caps with a 23-year-old who runs like the wind? There is no space in rugby so collisions become more important.

"Rugby now is a collision sport. World Rugby needs to find way to make it more fatiguing. There are various suggestions that need to be looked at. The ball needs to be in play for longer periods.

"Look at the game of rugby. It's 80 minutes and sometimes the ball is in play for 27 minutes. The longer the ball is in play the more fatigued players are, the more fatigued players the more space there is. There is a solution but we are never going to take away collisions in rugby."

Jones has also warned Scotland that there is more to come from his Brave Blossoms, starting with Wednesday's clash at Kingsholm.

"Next it's the most important game in the World Cup, against Scotland," he said. "We haven't just come here to make one splash in the pond, we are here to play a World Cup and we want to make the quarter-finals.

"If the players aren't excited after Saturday that would be a problem, they are excited. It's a quick turnaround but we are used to that."

Jones has made seven changes to his starting XV, with injured No. 8 Hendrick Tui replaced by Amanaki Lelei Mafi.

"Scotland are going to maul and high punt, it's probably not going to be a pretty game," he added. "We have to front up physically in the set pieces and if we do that we will put ourselves in the game.

"We've got slight variations in how we want to play. Test match rugby is about fronting up in the first 30 minutes, and if we are still in it after 30 minutes then I reckon we can win the game.

"The start will be super important, we have to start early, but that can be hard after winning the previous game.

"To borrow a cricket analogy if you score 100, when you come out in your next innings you have to work even harder."