The past two years have seen a vast improvement in England's limited-overs form, with a team that suffered an embarrassing first-round exit at the 2015 World Cup now top of the one-day international rankings.
The form of Eoin Morgan's side has been a huge boost to the England and Wales Cricket Board (ECB), who have staked a lot -- including a contentious rejigging of the domestic season -- on England winning the World Cup for the first time when the 2019 edition takes place on home soil.
But England's white-ball rise has been accompanied by a dip in their Test results, with Joe Root's men going down to a 4-0 Ashes defeat in Australia before a 1-0 series reverse in New Zealand.
England have prided themselves on being a tough Test side to beat in their own conditions but had to battle back to share a two-match series against Pakistan 1-1 after a thumping nine-wicket loss in the first Test at Lord's.
And Pietersen said one-day success was being prioritised to the "detriment" of England's Test-match form.
"I don't know which direction they want to go in," former England batsman Pietersen, who helped the side to a number of notable victories, said on Friday.
"We won a T20 World Cup, we won the Ashes home and away, we beat India in India a few years ago," added the 37-year-old ex-England captain, who scored over 8,000 runs including 23 hundreds in 104 Tests at an average of 47.28.
'Big Tests Will Continue'
"England haven't won a 50-over World Cup, I know that was the message a few years ago to do that and you can see they are driving towards that World Cup in England next summer, at the detriment of Test cricket. And I think it's sad and frustrating for us as players who have played over 100 Test matches," Pietersen explained.
"The public care a lot more about Test match cricket than they do about the shorter form of the game.
"The big series will continue to exist, the Ashes will be fine, India v Pakistan, Australia against South Africa."
England face Scotland in a one-day international in Edinburgh on Sunday before their World Cup build-up continues with a five-match home ODI series against oldest rivals Australia.
This trip sees Australia in action for the first-time since their tour of South Africa when captain Steve Smith, vice-captain David Warner and batsman Cameron Bancroft were suspended for ball-tampering.
Australia were on the receiving end of some alcohol-fuelled 'banter' relating to the scandal during a 57-run victory in their tour opener against Sussex at Hove on Thursday.
But as far as Pietersen is concerned, there is one way the team can quieten their critics.
"They have just got to win, when you win the media go with you, when they lose they hammer you," he explained.
"Australia are always the pantomime villain, no doubt the English are going to go after them, but that's the nature of the beast, they always go after us when we go there."
Pietersen may have represented England but the South Africa-born batsman will be playing against them for the Rest of the World in the Soccer Aid match at Old Trafford on Sunday.
A fan of passing football, Pietersen nevertheless expects the Rest of the World to employ long-ball tactics given their captain and striker is Usain Bolt, the multiple Olympic sprint gold medallist.
"The captain will be the goalscorer as long as he is quick off the mark like he always is," said Pietersen.
"He will be fed a lot of balls and if his left boot is firing he will score a lot of goals," he added ahead of a charity match raising money for the United Nations' Children's Fund.
First Published: June 9, 2018, 8:30 AM IST