The 41-year-old star and his wife Luisana Lopilato revealed Noah's devastating health battle in a joint statement on Friday (04Nov16) but referred to his condition simply as "cancer".
Since then, there has been reports the tot has been diagnosed with leukemia - a common type of cancer found in children - but Luisana’s sister Daniela told Argentinian journalist Tomas Dente that's not what Noah is struggling against.
“To tell you the truth, I’m devastated. This is very recent,” she said. "The only thing I ask is that you don’t speculate because not everyone has children and can understand what this means.
"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.”
Daniela added that Michael and Luisana are "broken in half" by their son's diagnosis.
The couple revealed their devastation at Noah's illness in their heartbreaking statement, which Michael posted on his Facebook page.
“We are devastated about the recent cancer diagnosis of our oldest son Noah who is currently undergoing treatment in the US," it read. "We have always been very vocal about the importance of family and the love we have for our children. Luisana and I have put our careers on hold in order to devote all our time and attention to helping Noah get well.
"At this difficult time, we ask only for your prayers and respect for our privacy. We have a long journey in front of us and hope that with the support of family, friends and fans around the world, we will win this battle, God willing.”
According to Argentinian publication La Nacion, while doctors initially thought Noah was suffering from mumps (a contagious viral infection), it was then discovered he was battling cancer.