Roy missed all four one-day internationals against the Black Caps, with his replacement at the top of the order, Dawid Malan, scoring 54, 96 and 127 to surely clinch his spot in the group to travel to India later this month.

Roy may yet be added to the squad for next week's ODIs against Ireland - Joe Root could be too, after a low-scoring series against New Zealand - to try and prove his fitness, with England required to confirm their World Cup 15 no later than September 28.

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Buttler stressed that loyalty will be a factor in selection, with Roy part of the World Cup-winning side four years ago and having amassed over 4,000 runs in 116 ODIs since making his debut in 2015.

Harry Brook would most likely take Roy's spot if England opted to make a late change.

Buttler said after his side's 100-run win over New Zealand at Lord's on Friday: "Nope [we are not settled on a final World Cup 15]. Obviously it changes and now you can let the dust settle on the series.

'We've reaped the rewards of being consistent with selection'

"We just have to find out (how Roy is). The biggest frustration for him is that he wants to be fit and playing, affecting games of cricket for England.

"You don't want to risk anything but at the same time, you do want guys to play cricket. That's our job, to play cricket and we all want to play.

"He's been working really hard to be fit and available but we now have a few days where we can regroup - the coach, the captain, the selectors - and just work out exactly what we need to do moving forward.

"We've tried to be a really loyal team and selection panel throughout. It's something [former captain] Eoin Morgan and [ex-coach] Trevor Bayliss started.

"We've reaped the rewards of being consistent with selection, so certainly you take the whole picture in. You can't just pick a World Cup squad from these four games because there's a lot of thought and process that goes into looking into people as a whole.

"That's been one of the hallmarks of selection but I think we can find out all the information over the next few days if we need to and make what will always be a really tough decision.

"We're blessed with so many good cricketers in the white-ball game at the moment but in a World Cup, you can only take 15."

'England have a duty of care with Archer'

Jofra Archer, who bowled the Super Over as England edged New Zealand on boundary countback in a thrilling World Cup final at Lord's in 2019, could head to India as a travelling reserve for this year's tournament after battling back from injuries.

However, Buttler says his side will take no risks with the fast bowler, who bowled in training during the ODIs against the Black Caps.

The skipper added: "He's been out of the game for a while.

"He's had his elbow and his back [injuries] and he's still a young man who's got a lot of cricket ahead of him.

"There's a massive duty of care to make sure that he's fully fit for the rest of his career.

"It's obviously exciting to see him in an England tracksuit and bowling, he's a superstar. But we'll find out more over time."

Watch England's three-match ODI series against Ireland live on Sky Sports, starting with Wednesday's opener at Headingley. Coverage begins at 12pm ahead of the first ball at 12.30pm.

Watch the Cricket World Cup live in full on Sky Sports between October 5 and November 19 with England vs New Zealand kicking off the competition in a repeat of the 2019 final.