"I am going to support Secretary Clinton tonight because I think it's important. I think she's capable, I think she'd make a great president. I think Donald Trump is just not fit for the job," Cuban said.

Cuban has openly supported Democratic nominee Hillary Clinton for the presidential race, and has publicly challenged Trump on everything from his net worth, to his ability to serve as president.

Tax documentation from 1995 revealed by The New York Times on Saturday uncovered that Trump reported a $916 million loss on that year's tax return, which would allow him to offset future income.

"The problem I have with what [Trump] has done is not that he hasn't paid taxes, honestly … It's that he won't own it and he won't explain it," Cuban told the " Mad Money " host.

Billionaire Mark Cuban told CNBC's Jim Cramer on Tuesday that he has also utilized the net operating loss deduction tax code used by GOP nominee Donald Trump . His issue is with Trump's refusal to "own it."

If Trump had just admitted that his business venture had failed and that he had learned from it, Cuban said, that would have been different. That would have fallen within the spirit of an entrepreneur.

"Do I take net operating losses? Yes. Do I use the tax code as it's written? Yes. But, there is a fine line between pushing the tax code and taking a risk and hoping there's an auditor you can negotiate with, and just saying 'you know what, I made $50 million or $100 million this year. If I'm paying $25 million in taxes, which some people might say is not enough, I'm OK with that," Cuban said.

According to Cuban, the example that a potential President needs to set for Americans is one that owns their failures and learns from them.

"If you can't admit a failure, you're not an entrepreneur. You are not a good business person. There's nothing brilliant about what you are doing. And then we would learn what is behind it. Obviously [Trump] is ashamed of it," Cuban said.

Cuban himself has learned from failure in his career. The self-made billionaire and owner of the NBA's Dallas Mavericks grew up in Pittsburgh, Pennsylvania in a middle-class family. His grandfather emigrated from Russia and supported the family by selling items from the back of his car. At 12 years old, Cuban showed early signs of entrepreneurship when he sold trash bags to save money for a pair of shoes.

After getting an MBA from Indiana University, he was hired to work for Mellon Bank. He only lasted for nine months before he left. He was then fired from his next job, and even quit the next one. Eventually, he found his way to Dallas selling software.

"We all fail and you only have to be right one time, and everybody tells you how lucky you are, right. But that's not what he's done," Cuban said about Trump.

Cuban clarified that he is not a Republican or a Democrat. He only wants people to vote. He also said he is not looking for a job in government, and has no interest in being an ambassador. He is simply an entrepreneur who wants to help other entrepreneurs.

Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank," which features Mark Cuban as a judge.