According to reports in Argentinian magazine Gente, three-year-old Noah will start four months of chemotherapy to tackle the disease.
Daniela Lopilato, the elder sister of Michael's wife Luisana Lopilato, opened up about her nephew's illness in the magazine, saying: 'If God wanted it discovered that way, it's because he wants to save Noah.
'Cancer is a horrible illness but we have faith in Noah being able to overcome this.
'We know he will. The time to start a long and very difficult treatment has come but it's got to be done.
'They say children are normally strong to put up with chemotherapy and my nephew is a warrior.'
The magazine also reported that doctors in Los Angeles confirmed Noah's illness by doing a liver biopsy following his initial examination at a clinic in Buenos Aires.
This further development comes after Michael posted a statement on his wife's official Facebook page revealing their devastation at the diagnosis.
Noah had travelled to the United States with his mother, Luisana, and his father due to concerns they had about his health. He was then diagnosed with a form of childhood cancer.
'We are devastated by the recent cancer diagnosis of our eldest son Noah who is currently in treatment in the United States,' Michael wrote.
'We've always talked a lot about the importance of the family and the love we have for our children.
'Luisiana and I are going to spend all our time and attention to help Noah to get better, by suspending our professional activities for now.'
'During this difficult time, we ask that you pray for him and please respect our privacy. We have a long road ahead of us and we hope that with the support of our family, friends, fans around the world and our faith in God, we can win this battle.'
According to Perez Hilton, Noah's doctor initially assumed Noah had mumps, but after looking into his health further, the cancer diagnosis became clear.
In addition the the magazine report, Noah's aunt, Luisana's sister, has previously spoken out about his diagnosis.
Daniela reported to an Argentinian television station that Noah's diagnosis has caused the family to be 'broken in half'.
She was unhappy about the rumours circulating about the type of cancer Noah has, saying:
'Michael and my sister will publish more statements and I can't say anymore but it's not leukemia or the central nervous system as people are saying. That's all I can say.
'The only thing I ask if that you don't speculate because not everyone has children and can understand what this means.'
Support has flooded in for the family, with messages from celebs including Shannon Doherty, who was diagnosed with breast cancer last year.
'I can't even begin to touch that one, to be honest, because it's a 3-year-old. I would imagine your child having cancer is devastating as a parent,' she said to ET Online.
'Just trust in your doctors. Make sure you have amazing doctors, a great team, and know that organizations like the American Cancer Society [and] Stand Up to Cancer, they are doing so much good for cancer. And [there is] so much research that we have much better chances now,' she said.
'Stay positive. That positivity, that outlook on life that you can get through something, it actually does get you through.'
Sharon Osbourne tweeted her support for the family, offering her prayers.
Sending positive thoughts and prayers to @MichaelBuble and Luisana for their son Noah— Sharon Osbourne (@MrsSOsbourne) November 4, 2016
Just last year, Noah was placed in hospital after suffering serious burns when he climbed onto a kitchen counter at home and burned himself with boiling water.
Fortunately, Noah didn't need serious surgery or skin grafts, but did need to change his dressing daily as his skin healed.
Michael was in the US at the time, and left immediately to see his family.
The family welcomed their second son, Elias, in January 2016.
We wish the Bublé family all the best at this difficult time.