Ireland coach Joe Schmidt believes rookie Ross Byrne will seize his World Cup chance in Saturday's game against England at Twickenham.

The Leinster fly-half will make his full Test debut and win a third cap, with Ireland not risking Johnny Sexton after Joey Carbery's ankle injury.

"Ross has trained really well and it's not his debut, he's had time with us before," said Schmidt.

"We've got a lot of confidence in him - he's built his way through the season."

Carbery could well miss the World Cup after damaging ankle ligaments in the 29-10 victory over Italy in Dublin on 10 August.

Byrne and replacement Jack Carty can now make their case for World Cup selection on Saturday, with head coach Schmidt assessing all his fly-half options.

"I thought Ross was maybe not as impressive as Jack early in the season, and I think those two have become really important to us," he added.

"Joey has done well this week. Johnny, he's fine, but he missed a bit of time with his thumb, so he's a little bit behind and we know how well he plays for us. We don't feel that he needs a lot of time with the experience that he's got.

"So, for us, the guys that need the time are probably Ross and Jack and they've got the opportunity to do that this weekend, that they'll share a bit of time, I'd say, in the middle."

Frontline fly-half Sexton has been recovering from a thumb sprain, and Carbery's ankle injury has whittled down Ireland's playmaking options for their World Cup warm-up encounters.

Ireland have also been handed added motivation ahead of the England clash with confirmation from World Rugby that a win would see Schmidt's men ascend to the top of the world rankings for the first time in their history.