What this CEO has meant to golfer Jordan Spieth

Jordan Spieth
Jessica Golden | CNBC

This offseason, Jordan Spieth isn't just practicing his golf swing, he's also getting schooled in business by Under Armour CEO Kevin Plank.

The two-time majors winner said he has a unique relationship with Plank and takes full advantage of getting a front-row seat at one of the fastest-growing sports apparel brands.

"People go through their lives for 20 years trying to go up the chain where they can sit in the same room and talk to Kevin," Spieth told CNBC in an event in Boston unveiling Beantown's first Under Armour store.

As the face behind Under Armour's golf line, the 23-year-old realizes his good fortune. "I certainly don't take it for granted," he said. "I take advantage of it asking him questions and picking his brain."

Spieth says they talk constantly about how to grow UA'S golf business and that Plank has also taken an interest in Spieth's goals outside of golf — whether it's charity work or business work.

"I'm very lucky he's so open to help and really preaching that family motto that certainly transcends throughout the company," he said.

While this year has seen tumult in the golf industry with Nike dropping its equipment business, Adidas putting TaylorMade up for sale and many big box golf retailers like Sports Authority and Golfsmith closing, Spieth remains optimistic. "It's certainly competitive," he said. But "UA has so much room to grow in this space. They are still so young even through their growth has been on top of the charts."

The Dallas native said that underdog mentality is what attracted him to the brand. "I love the young, fearless nature that Under Armour displays." Spieth said he doesn't feel pressure to grow UA's golf business too fast, saying that Plank has set the tone for him. "He's been very relaxed and letting things take shape, find the weak spots and putting his attention there."

When Nike announced it's getting out of the golf equipment business, Spieth said that caught many people off guard. "That was a bit of a shock when that came down," he said. However, Spieth said his PGA tour colleagues sponsored by Nike, most notably, Tiger Woods and Rory McIlroy, enjoy the flexibility of playing with what they want. Spieth says they frequently talk shop to each other about the different equipment brands and clubs.

Despite that, Spieth has no plans to give up playing with his Titleist clubs. "I have played Titleist my whole life, so I just trust it," he said. Acushnet, which owns Titleist, had an IPO this month. Spieth said he didn't get any stock with the offering but he imagines he'll be a shareholder at some point.

"In golf trusting what you are wearing and playing with is first and foremost so you don't have to worry about anything but your game."