The star third baseman tweeted Tuesday night that his hip surgeon has cleared him to play in rehabilitation games, a move that angered Yankees general manager Brian Cashman, according to ESPN.com.
"You know what, when the Yankees want to announce something, (we will)," Cashman told the website.
"Alex should just shut ... up," the GM said, punctuating his comment with a profanity.
Cashman added that he planned to get in touch with Rodriguez right away.
The general manager did not respond to calls from The Associated Press.
Rodriguez had left hip surgery on Jan. 16 and has been working out since May at the Yankees' Tampa complex. The three-time AL MVP took swings in a simulated-game situation for the first time on Monday.
On Tuesday night, he posted a message on Twitter: "Visit from Dr. Kelly over the weekend, who gave me the best news — the green light to play games again!" Rodriguez also posted a photo of himself and Dr. Brian Kelly, who performed the operation in New York.
Rodriguez did not stop to speak with reporters Wednesday when he drove into the team's minor league complex in Tampa, Fla.
"I will continue to work hard until my efforts get me back in pinstripes and help my team win," Rodriguez said in a statement. "The tweet was pure excitement about Dr. Kelly's prognosis."
Cashman recently said Yankees doctors have not yet cleared A-Rod for minor league rehab games.
"I don't tweet, and I really don't follow Twitter. So I probably don't really know much of what is going on. As far as I know he has not been cleared," Yankees manager Joe Girardi said Tuesday night after his team's 4-3 victory over Texas.
"There's always a chain of command with injuries. There has to be and that's the process. It goes through our training staff, our doctors and our GM and then it goes to me. I'm down on the totem pole."
Before the game — and Rodriguez's tweet — Girardi said Rodriguez "is making progress, which is good."
"He's in sim games until they decide he's ready to go out on a rehab. It's not yet," the manager said.
New to Twitter, Rodriguez sent his first tweet on May 31. He is expected to return to the Yankees around the All-Star break, shortly before he turns 38.
Benched by the team as he slumped through last year's playoffs, A-Rod has been in the news a lot lately even though he has spent almost no time with the Yankees this season. He is among the 20 or so players who may be disciplined by Major League Baseball for their links to the now-closed Miami anti-aging clinic, Biogenesis of America. A first offence under baseball's drug program results in a 50-game suspension and a second in a 100-game ban, but players don't serve penalties for a first offence until after any grievance is decided.
Rodriguez admitted in 2009 that he used performance-enhancing drugs while with the Rangers from 2001-03. As baseball's highest-paid player with a $28 million salary this year, he would lose $7.65 million during a 50-game ban if it is served this year.
AP freelance writer Mark Didtler in Tampa, Fla., contributed to this report.