England insist their surprise move to replace Alex Hales with Moeen Ali as Alastair Cook's opening partner is far from set in stone for the World Cup winter.

Hales will begin the road to Australia and New Zealand on the sidelines for Friday's first instalment of unbroken 50-over cricket in the next four months.

Selected as Cook's power-hitting foil in last summer's series defeat against India, the 25-year-old will find himself here watching Moeen partner the captain in the first of two warm-up matches against Sri Lanka A.

Cook described it as an "incredibly hard" decision.

He added: "We really wanted to have another bowler in our top six, and Mo gives us that option.

"It's a real tough call on Alex ... but this is nowhere near our final decision."

Coach Peter Moores explained the same rationale, Ian Bell pencilled in at number three and therefore no room for Hales in the XI chosen less than a week before the first of seven one-day internationals against Sri Lanka.

"Alex hasn't done anything wrong ... but it is for us to look at options and see where we are," said Moores.

Cook concedes that, in an "ideal world", England would know not only their favoured opening partnership but the rest of their best team too as they fine-tune preparations for the World Cup.

But as they first of all eye some "revenge", in Cook's words, for narrowly losing a sometimes tetchy series at home to Sri Lanka last summer, he is adamant it makes no difference to him whether he opens with Moeen, Bell or Hales.

The latter, the world's leading Twenty20 batsman, made his ODI debut less than three months ago but - after two 40s - mustered only single-figure scores in his two other innings.

Moores said: "Alex has progressed quickly.

"The fact he has managed to climb to number one in the world as a T20 player means there is a lot of talent there - and explosive talent at that.

"He had some exposure in the one-day arena against India, where he would have learnt a lot.

"When you play international cricket and come up against the same team time and again, people will always find a kink somewhere - and the key is how you adapt.

"India started to bring the ball back into Alex and bowl spin at him, so he has to decide what else he is going to come back at them with."

Hales still has a route to the World Cup, though.

"There are certain places for lads to fit in and that is about taking opportunities," said Moores.

"This tour is about winning - and people taking their games on.

"We've got two practice games to try and win but to also look at some options we've got.

"We've then got a tough decision to pick the ODI team - and it is very tight."

Cook has borne much criticism for his mediocre strike rate, among pundits who believe England must drastically up their game to compete with the best.

But there will be no panic from Moores, even after India's Rohit Sharma set a new ODI benchmark with a world-record 264 for India against Sri Lanka just last week.

"We're trying to get a batting unit that scores above par on a given surface," said Moores.

"If par is 270 and you get 290, then you're playing well.

"To do that, it is not as simple as saying to guys 'Go out there and whack it'.

"In that Rohit Sharma innings, I think I'm right in saying they were 124 from 25 overs and (then) score 281 in the last 25."

Moores reasons therefore that England too could top 400 - in the right conditions.

"I think anybody can get any score," he said.

"We make no excuses. We know where we've got to move to and we're on that journey - to win a series here, I hope, and then carry that form into Australia."

Primary among Cook's many virtues is his resourcefulness, and Moores added: "He's been around the block a lot.

"He's been under pressure before and he's often responded to that pressure really well.

"We know he's a steely character and a very good player."

England's opening partnership is not the only one as yet undecided, Sri Lanka captain Angelo Mathews acknowledging the hosts' middle-order veteran Mahela Jayawardene may be promoted in this series.

One man very definitely out of the equation for good is, of course, Kevin Pietersen - Cook and Moores both stressing England have "moved on" from the controversy surrounding the publication of the sacked batsman's autobiography.

Moores has read Pietersen's book, which features claims of a "bullying" culture in the England dressing room during the tenure of former coach Andy Flower.

Moores said: "It's one side of a story. That's what it is.

"I read it for the reason that I'm always interested in what other people think.

"If totally in that book is exactly what he was thinking at the time, nobody really knows ..."

England (possible, v Sri Lanka A): AN Cook (Captain), MM Ali, IR Bell, JE Root, EJG Morgan, JC Buttler (wkt), RS Bopara, CJ Jordan, JC Tredwell, ST Finn, HF Gurney