The 70-year-old, who returned to club management at the tail end of last season following a short retirement, had to undergo an operation and was only recently given the all-clear to begin his pre-season duties with the Blues.
Former Tottenham Hotspur and Portsmouth boss Redknapp saw test results for cancer come back negative last week, but he says that he was left fearing for his life at one point following previous health complications.
"I could feel it in my body - I knew it wasn't right," he told The Sun. "This is the first time I've been properly worried. I knew I didn't feel good, you know when something isn't right, but it was Sandra who pushed me to the doctor in the end. I am lucky, I know that because it could have been malignant.
"They cut it out, there was no other option. Once they did that I was up and about after a couple of days. I am relaxed about it now because what can you do?"
Redknapp also talked of his hopes of taking Birmingham up to the Premier League in his first full campaign at the St Andrew's helm, having achieved his mission of keeping the club in the division last term.