A.J. Pollock grabs his arm after scoring on a hit by David Peralta against the Royals on Friday. (Jae C. Hong/AP)

A.J. Pollock, the best MLB player you don’t know, dove headfirst into home plate in an exhibition game, and it could cost him and the Arizona Diamondbacks big time.

The all-star center fielder fractured his elbow when he used his right arm to brace his slide in Friday’s exhibition game against the Kansas City Royals. He’ll need surgery and there’s not yet a timetable for his return, Manager Chip Hale said.

Via MLB.com:

“It was just one of those things where I was going to dive head-first some time this season,” Pollock said. “It wasn’t a dive, it was more kind of [on] the pop-up, I felt something. I’ve done it before, so I kind of didn’t have a freak-out. I knew what happened. Lot of frustration.”

Pollock, 28, is coming off a career season where he finished ninth in Wins Above Replacement (7.42). He hit 20 home runs, 39 doubles and stole 39 bases — the only player to do so. He also batted .315 and earned a Gold Glove in center field.  (In Barry Svrluga’s March 4 profile in The Post, he attributed that versatility to his days playing youth basketball and soccer. Take note, kids.)

The surgery will be performed at a to-be-determined date by Don Sheridan, the Diamondbacks’ orthopedic hand and upper extremity specialist, according to MLB.com.

This was the same elbow that had been bothering Pollock since March, and at one point it almost led him to start the season the disabled list. (This was Pollock’s first MLB game of 2015). It’s also not the same elbow that he fractured in the spring training of 2010, and missed that entire season. Given Pollock’s injury history and the well-documented injury risks associated headfirst diving — along with the non-existent rewards of doing so successfully in a meaningless game — this seems like a play that could’ve been avoided.

“If he goes feet-first, he’d be OK,” Hale said, “but the problem is the way the play played out. If he goes feet-first, he might have gotten his leg broke by the catcher. It’s just unfortunate.”