Going through a purple patch, Kohli has often being compared with England batsman Joe Root, which Pieterson feels isn't a fair comparison.
"Kohli is as good as it gets. He is right up there. Root has good numbers, but it's unfair to even compare Joe with Virat because his numbers are just phenomenal," Pietersen was quoted as saying by 'The Cricketer' magazine.
"He plays so aggressively - sometimes it's like - are you serious? The way he makes big runs for his team so often is just remarkable," he added.
"He just has that ability to rotate the strike and find boundaries. His ODI record is a joke. Such an old head on young-ish shoulders."
England will be up against a formidable spin trioka of off-spinner Ravichandran Ashwin, left-armer Ravindra Jadeja and leg-spinner Amit Mishra during their bilateral series against India.
Pietersen said England need to watch out for the doosra from Ashwin, who has been in red-hot form, picking up 153 wickets in 22 Tests at home.
"When I've played against him, I could pick his doosra, so I was OK. But if England's batsmen can't pick his doosra they'll have issues. The low bounce might make it harder, but that's part of the challenge of playing in India.
"Batsmen have got to find themselves a boundary option in India. It's all about rotating the strike and manoeuvring the field. I was OK in India. I enjoyed it there. I made plenty of hundreds there," he added.
The first match of the series will be played at Rajkot from November 9.
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