Major League Baseball spokesman Michael Teevan said the commissioner's office is looking into the matter. Last month, the Boston Red Sox were fined by MLB for using an Apple Watch to relay signs to hitters.
Arizona opens the NL Division Series on Friday against the Los Angeles Dodgers.
Prieto said Thursday that he didn't use the watch for any illicit purpose and it was on "airplane mode" during the game on Wednesday night. That setting shuts off any of the watch's communication abilities.
The former big league pitcher is an extra coach who also serves as interpreter for the Diamondbacks. He said he knows having the phone during the game violated MLB's rules. He said he apologized to manager Torey Lovullo and volunteered to turn the phone over to MLB officials.
"It was just an honest mistake," Lovullo said. "We asked, found out, and talked to Ariel, and that's what he told us. And in no way did it impact the game, and in no way is it going to impact the game tomorrow. It's just not something we do or believe in."
The Diamondbacks beat Colorado 11-8 Wednesday night and Prieto was shown wearing the watch during the game's telecast.
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