NFL alum has 1 simple lesson for the NFL draft class: Learn how your money works before it's too late

Former NFL player’s warning for rookies — don't count on next season's...

Former New Orleans Saints wide receiver Marques Colston knows that, even at the most elite level, a career in professional sports doesn't mean lifelong financial stability. An alarming number even go bankrupt.

Some star players earn millions of dollars each year, like Detroit Lions quarterback Matthew Stafford, who makes $27 million, the highest salary ever in the NFL. Colston started his decade-long career in the NFL as a rookie making far less, the league minimum, which, when he was drafted in 2006, was $275,000. (It's $480,000 this year and rises over time.)

Still, because he knew those contract earnings wouldn't last forever, he made sure to plan for the future. In 2012, while he was still playing, he started angel investing in start-ups, too.

Colston retired after the 2015 season and started a digital marketing agency called Dynasty Digital. He collaborated with professors at the Columbia Business School to develop courses through which he could pass on what he learned to other professional athletes. Since what pro athletes earn can vary considerably, he says, they need tailored financial advice. And everyone needs to be reminded to put something away: "Save as much as you can, because tomorrow's not promised," he says.

To hear his money advice for the NFL draft class, watch the video above.

Don't miss: Super Bowl champ Marques Colston says successful people all share one trait: 'Irrational confidence'

Like this story? Subscribe to CNBC Make It on YouTube!

How LeBron James inspired former NFL player Marques Colston to go into business