The 31-year-old Aregentine midfielder has undergone chemotherapy after having surgery following the discovery of a tumour.
But it was detected following an accidental collision with Sagna on the final match of the 2012-2013 season at St James' Park.
After the challenge, Sanga had a scan which led to the discovery of the cancer.
In an interview with TYC Sports in Argentina, Gutierrez said: "I had a very hard collision with Sagna in the area of the pubic bone and the genitals.
"From then I had a lot of pain that wouldn't go away. It was the last game of the season. I spoke with the doctor straight after [the game] and he said: 'If it doesn't hurt then don't worry I don't think it is anything [to worry about].
"Then it was holiday time and I felt the pain more in the testicle. "We started the pre-season, the season started and in September, October. I noticed that the testicle started to become inflamed.