The 26-year-old suffered the injury when struck on the ribcage by a Glenn McGrath delivery as he top-scored with 82 in England's defeat in the opening match of the triangular series at the MCG here Friday.
He was adopting the tactic of advancing at McGrath, a ploy he also used during the Test series, when he was hit.
Although he continued to bat after the blow, he didn't look comfortable and was dismissed a short time later.
Pietersen is returning to England and his recovery time is expected to be at least 3-5 weeks.
With the World Cup just eight weeks away, it is an untimely injury for Pietersen, but he expects to be fit for the Caribbean tournament.
"I'll be getting myself as fit as I can," he said after Friday's game.
"I've never played in the World Cup before so I'll be in the Caribbean if selected.
"I'll just have to bide my time but I'm a pretty quick healer, so I'll get myself as fit as I can as quick as I can and I'll be champing at the bit to get out to the Caribbean."
Pietersen, who averages more than 50 with the bat in one-day internationals in the struggling English limited-overs side, said he knew he was in trouble as soon as the delivery struck him.
"I've never been hit so hard," he said. "I've been hit a few times and I've gone 'Oh yeah, that will be all right with a bit of ice', but when this one hit me I couldn't breathe for a few minutes and I knew it was a little bit more serious than the other ones. It did restrict my breathing and my strokeplay."
Pietersen was dismayed at having to leave his teammates without having enjoyed a win since arriving in Australia in early November.
"Distraught. Absolutely distraught," he said. "It's not how I planned it out. I planned it out to give it a real good go and to draw a line after what happened after the Ashes.
England captain Michael Vaughan admitted Pietersen's loss was a big blow for an already struggling side.
"When it rains it pours," he said. "There are not many Kevin Pietersens in the world, let alone in England."
England were expected to name a replacement for Pietersen within 24 hours.