Ireland scrum-half Craig Casey says it would be "unbelievable" to make his World Cup debut against Tonga in Nantes if afforded the opportunity.

Ireland will hope to build on their thumping 82-8 win over Romania when they face the Tongans on Saturday.

"If I get the chance now I'll really look forward to it," said Casey.

"When you're part of a squad only 23 can play so going into a tournament you know you're not going to play every minute.

"Every player knows that. You have to be ready for your opportunity and when it does come you have to take it with both hands and try and cement your place for the weekend after.

"Everyone is itching to go, even the lads who played last weekend are itching to get back on the field so there's a real buzz around the squad."

'We have to go up another level'

Despite the emphatic nature of Ireland's opening victory, Andy Farrell's squad have been working hard to identify areas for improvement.

"There were bits we weren't really happy with so we're trying to put those into place," continued Casey.

"We know we have to go up another level. We've played Fiji and Samoa over the last year or so and we know how tough the Pacific Island teams are.

"It's going to be a tough test this weekend and we have to be at our best.

"They've got some seriously good players, that have come back to Tonga having shown their hand in previous World Cups, and have a lot of experience behind them.

"We know they're going to be physical but they've got some really good ball players as well.

"[William] Havili at 10 has a very good boot and he's a very smart player so he'll probably put them around the place nicely and get their big ball carriers into the game.

"I obviously know Malakai [Fekitoa] very well from his time at Munster so I know how physical he can be."

'Buzz has increased'

Casey was part of the Munster squad who won last season's United Rugby Championship, an experience which the 24-year-old believes will stand him in good stead if he is given the chance to add to his 12 international caps.

"To win a trophy with Munster was brilliant, a huge goal ticked off. Coming into a World Cup scenario it gives you confidence that you have played in big games.

"It's exactly where you want to be as an Irish rugby player, at a World Cup, involved in this group.

"We've all talked about how good the buzz has been for the last two or three years, it's definitely increased since we got over here.

"The excitement levels in the group are brilliant, but also mixing it with a lot of hard work. It's a very enjoyable place to be."

While the squad's focus is fully on this weekend's match against Tonga, Casey revealed that the squad came together on Sunday to watch the game involving their other two Pool B opponents, South Africa and Scotland.

The Springboks began their defence of the Webb Ellis Trophy with an 18-3 victory in Marseille and will face Ireland in what is expected to be a titanic encounter on 23 September.

"We all watched it together," Casey said. "There was a good 25 of us watching it in the team room.

"It was a very physical game. Both teams played well in the first half, then South Africa kind of outmuscled them in the end.

"That's what we're expecting in a few weeks' time, a physical encounter."