Diamondbacks general manager Kevin Towers said Friday that Eaton had an MRI that revealed a small tear in the fibers around the ulnar collateral ligament. Eaton had been bothered by a sore elbow for a couple of weeks and the Diamondbacks had recently given him a couple days off.
"Of course you like to play through it as a competitor," Eaton said. "You don't like to be in the training room at all and get that type of attention. A couple of guys I talked to talked me in to going in and getting it checked out. I was still thinking it was nothing. I've never had any arm problems my whole life."
Towers said Eaton, expected to be Arizona's starting center fielder and leadoff hitter, will be shut down for four weeks and the best-case scenario for his return would be in six weeks, but could be as long as two months.
Eaton said he wants to come back sooner.
"I'm sitting here today saying it's not going to take me that long," he said. "I'm going to do at all costs to get back quicker. I put all my faith in the doctors but at the same time for me there's an aspect where I want to try to get back a little sooner and try to push things a little bit. We'll be smart with it, of course, we're not going to do anything stupid with it. But I'm definitely going to try to do a speedy recovery for sure."
Eaton played 22 games for the Diamondbacks late last season before he was hit by a pitch and broke his right hand.
The speedster was to play a major role in Arizona's plans to change its offensive style and his absence leaves the team thin in the outfield, with Cody Ross -- projected to start in right field -- unlikely to be ready for opening day because of a calf strain. That leaves the team with a probable outfield of Jason Kubel in left, A.J., Pollock in center and Gerardo Parra in right.
Eaton hit .390 this spring with 23 hits and 10 RBIs in 59 at bats.
The scrappy outfielder sent a message via Twitter thanking his supporters.
"You know that I will work my butt off to get back in there," he wrote. "It will be sooner than later."
Eaton said that he visited team doctor Michael Lee 1½ weeks ago and, when his discomfort persisted, he underwent an MRI as a precaution, only to discover the problem was worse than he expected.
"It's going to be tough to see the guys go and have fun every day but I guess it's all part of the game," he said, "but it's going to kill me for sure."
The Diamondbacks will shut Eaton down completely for up to two weeks. Eaton can hit after that but won't be allowed to throw for four weeks.
"It doesn't bother him to hit and he can throw. It only bothers him when he really lets go, a long throw," manager Kurt Gibson. "He will get a lot of at-bats. He will probably stay in extended (spring training). When he gets into that window where he can throw we will send him out for a 30-day assignment. The earliest scenario is May 15th."
"I wouldn't rule Cody (Ross) out," Gibson said. "He's been getting at-bats. He's not going to run but he will get eight to 12 at-bats. We have a camp day. It's possible he could be ready in a short period of time."