The doctor has defended his actions claiming he saved the man's life.
John Patterson, who performed the surgery in 2007, said that during the operation on 64-yr-old, Phillip Seaton, he discovered a rare and deadly cancer.
"What I saw was not a penis. What I saw was cancer," Dr Patterson told the court in Shelby County, Kentucky.
However, Mr Seaton was appalled at the doctor's decision to amputate without consulting him, or giving him the opportunity to seek a second opinion.
His wife Deborah is also a plaintiff in the suit, which seeks unspecified damages for "loss of service, love and affection", the Mail said.
In earlier testimony, Seaton had described the moments after being told part of his penis had been removed.
"I pulled the dressing down, and I didn't see nothing," said Mr Seaton. "Then I came out of the restroom and I said, "I'm getting the hell out of this damn hospital."
Dr Patterson, in his defence, testified that the cancer prevented him from inserting a catheter into Seaton's urethra, and he was concerned about the possibility of kidney damage from urinary retention.
Although his wife was in the hospital waiting room, the doctor said he did not consult her because she had not accompanied her husband to office visits or into the pre-operation area, which he thought was unusual, according to the newspaper.
Mr Seaton then testified that had the doctor consulted her after finding the cancer, she would have advised him to halt the surgery and woken up her husband.
"It's his body," Mail quoted her as saying. "He should have a say in it."
Kevin George, Mr Seaton's lawyer said, the document had been read out to Seaton because he cannot read. The jury of eight women and six men was shown graphic images.
George presented four photographs of Mr Seaton's groin saying, "You can see there's nothing there." He told jurors that Mr Seaton "doesn't feel like a man anymore".
"The spark is gone out of his life. He used to be such a happy person," David Seaton, Phillip's brother said.