Even for a 22-year-old reigning Masters winner with a rocket-caliber launch to the top world's ranking, Jordan Spieth is playing a lot of golf. If Spieth were to play in the Arnold Palmer Invitational (he is not), it would be his eighth tournament of the year.

By comparison, Jason Day, the world's third-ranked golfer, has played in four tournaments this year headed into the API. Day climbed to the top of the world rankings for four weeks last year and said he found the kind of schedule Spieth has been keeping to be alarming.

"You know, dealing with all this stuff, it is difficult," Day said. "I think the biggest thing for him is to embrace the challenge of being No. 1, because if you look in the Hall of Fame there's no one out there that is terrible, and for him, I mean, he's got such a long career in front of him.

"I'm worried about him, because I don't know if he's playing too much and he's doing too many things with golf and sponsor obligations that he may get burned out and go through a rut where he doesn't want to be on the golf course for a while."

After golfing at the University of Texas, Spieth turned professional in 2012 and officially became a full PGA Tour member in 2013 when he won the John Deere Classic in July. About two years later, Spieth became the second youngest golfer to ever win the Masters while also setting a record for the most birdies in the tournament with 28.

Spieth's schedule this season made headlines before Day expressed his concern, and he admitted in January to being "very tired." At that time, he had played five tournaments on multiple continents since October and was preparing to travel to Singapore. Spieth's activity has been lucrative, as he won a total of $22 million in prize money in 2015, which does not include his endorsement deals with Under Armour, Coca-Cola and more.

"It won't be something I'll do in the future, to bounce back and forth from Asia as much as we did, or Australia," Spieth said in January. "I'm very tired. As a team we're beat up mentally and physically. I'm not 100 percent right now. It shows in certain places."