Brandon McCarthy says he won't wear the MLB-approved protective cap because he doesn't believe it is ready.

It's a surprising response from the Arizona Diamondbacks pitcher, who is arguably one of the main instigators for the caps creation.

While pitching for the Oakland Athletics in 2012, McCarthy was struck in the head by a line drive from Los Angeles Angels' Erick Aybar.

Although leaving the field with his own strength, he later deteriorated and needed life-saving surgery to to relieve pressure on his brain caused by internal bleeding.

But after testing the cap during a catch and running session, McCarthy doesn't believe the cap is ready.

"I won't wear it in its current form," he told ESPN.

"The technology is there," he said. "It helps. It's proven to help. But I don't think it's ready yet as a major league-ready product. And I told them that. I told them that's where it's at."

McCarthy has helped in the development of the cap for months but informed both the MLB and  4Licensing Corporation subsidiary isoBlox before the announcement that he wasn't happy with the design.

The pitcher says the cap is just too big and noticeable and not yet a viable alternative to an ordinary cap.

"You can't pitch a day game in St. Louis wearing it, or a day game in Baltimore," he said. "I've thrown in it in optimal conditions, inside where it's cool, and your head gets itchy.

"[So] if your head moves a tick, you feel it. You notice it.

"Nobody wants this to work more than me. But we tried to take this as far as we could and see if it's something that could work, but it just wasn't there."

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