The South Africa-born shotmaker has been the mainstay of England's batting during their series with Sri Lanka, equalling his Test best 158 in the drawn series opener at Lord's and striking a man-of-the-match winning 142 in the hosts' six-wicket second Test win at Edgbaston.
Pietersen, who scored 158 in England's Ashes-clinching draw at The Oval in September, is now on the verge of becoming the first batsman to score hundreds in four successive Tests in England.
"We saw last week the way Kevin can play," Flintoff said Thursday. "He looks in fine touch. We should just leave Kevin to play. He's got his own method which works for him.
"He's obviously a special talent but we can't rely on him too heavily," added Flintoff of the 25-year-old Hampshire batsman.
"But within the side we've got some other good players. Alastair Cook did fantastically at Edgbaston, in the second innings his 34 not out was crucial.
Marcus Trescothick scored a hundred in the first Test and then there's Andrew Strauss. As much as Kevin played well last week, there are some other very, very good players in our side."
Victory at Edgbaston left England 1-0 up in their three-match series with Sri Lanka ahead of the third and final Test starting here Friday at Trent Bridge, where Pietersen began his career in England with Nottinghamshire five years ago.
One feature of the series thus far has been Pietersen's duel with Sri Lanka off-spinner Muttiah Muralitharan.
And Flintoff also told reporters at Trent Bridge here Thursday that Murali, his former Lancashire team-mate, had become even harder to face during the past two years. "He's tricky, he's got all the different varieties of balls, and over the past two years he's got better.
"When he played at Lancashire he probably didn't have as many tricks up his sleeve as what he's got now.
"He's become a slightly different bowler. He has the ability to spin it genuinely both ways, he's got a flipper now, and all sorts.
"A side with Murali in it, anything can happen. He's taken 13 wickets in two Tests. We are not going to take it lightly, he one thing we can't be is complacent," Flintoff added.
"We've got to look after our game and be professional in the way we approach playing Sri Lanka."