During that time, he formed ideas about money that he still carries with him today.
"I had a counselor once tell me that I had a poor mentality. I think like a poor man," he said.
"I'm OK with that," Gbajabiamila added. "Because it keeps me humble.
"It keeps me staying within a framework that allows me to invest in my future."
Gbajabiamila's parents, who emigrated from Nigeria in 1974, were both business owners. His father owned a plumbing business and his mother had her own hair salon. They instilled in him the importance of saving money.
"I can hear them in their Nigerian accent: 'You better save for a rainy day, save for a rainy day,'" he said. "And to me that was the foundation of my financial literacy."
After graduating from college, Gbajabiamila spent five years in the National Football League as a linebacker and defensive end with the Oakland Raiders, San Diego Chargers and Miami Dolphins.
During that time, he really learned how to manage and invest his finances.
"I still remember my first year — $225,000 in 2003," Gbajabiamila said in a March interview with CNBC. "I was like, 'Oh my goodness, this is a lot of money,'" he added. "What am I going to do?"
When he retired from the game in 2008, he had about $300,000 in savings.
However, Gbajabiamila struggled for the next few years before joining the NFL Network in 2012. In 2014, he became a host of "American Ninja Warrior" and he now is adding author to his resume. His book, "Everyone Can Be a Ninja," comes out this month.
Gbajabiamila, a member of the CNBC Invest in You Financial Wellness Council, said it's easy to "get sucked into the lifestyle" but he tries to stay mindful about his finances.
"Money, to me, really is a tool," he said.
"When you grow up and you have a humble beginning, you realize there's certain things you can and cannot afford," Gbajabiamila said. "And I think that perspective really keeps you in a safe zone.
"Live within your means."
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Gbajabiamila also believes it's important to overcome your fears to achieve your dreams — financial and otherwise.
Giving into fear is "how we sabotage ourselves," he wrote in his book.
"Greatness is hard; mediocrity is so easy. … To pursue your dreams, to chase greatness, is a trial. It's a test of character, strength, and will. It's not meant to be easy."
Disclosure: NBCUniversal and Comcast Ventures are investors in Acorns.