"It was a pretty dark time," the 29-year-old told the Mail on Sunday newspaper. "The infection was really bad.
"I was told by the surgeon it was career-threatening so for two days I sat there on a drip thinking: 'Where am I going to go from here?' Things looked pretty bleak."
Pietersen took a while to recover before returning to the middle order for the tour to South Africa [ Images ] in November.
Although England regained the Ashes with a home victory over Australia [ Images ], 2009 proved a less than perfect year for Pietersen especially after he had quit as captain in January following a breakdown in his relationship with then-coach Peter Moores.
"After what I went through last year, I did fall out of love with the game," Pietersen said on Sunday. "But I am back in love with it now."
The South African-born batsman is due to line up for England in Southampton on Tuesday for the start of a five-match series of one-day internationals against Australia.