Sheffield, now with the Detroit Tigers, said Monday that A-Rod is heading into the 2007 season with a clear mind, finally having unloaded the mounting stress of concealing his fractured relationship with shortstop Derek Jeter.
"I guarantee you one thing, and I say this right now: Alex is going to have the best year since he's been [with the Yankees]," Sheffield said. "I think what he did, stood up, that's what's going to get him over the top. He expressed how he felt. He was honest, and that goes a long way. I guarantee you, when he went home, it was a peaceful night."
Last month, Rodriguez admitted to reporters that he and Jeter are no longer as close as they used to be.
"We were like blood brothers," Rodriguez said on Feb. 19. "You don't have to go to dinner with a guy four, five times a week to do what you're doing. It's actually much better than all you guys expect, but I just want to let the truth be known."
The 31-year-old Rodriguez batted .290 with 35 home runs and 121 RBIs in 154 games for the Yankees last season, but he suffered through several extended slumps. He also struggled in the postseason, going 1-for-14 in the ALDS loss to the Tigers.
Sheffield, 38, has spoken with Rodriguez periodically over the winter. Sheffield believes that the persistent public speculation over Rodriguez's relationship with Jeter contributed to A-Rod's troubles.
"He really wanted to say these things a long time ago," Sheffield said, "but Alex is just a passive guy in that area. He didn't want to touch that subject. That could be borderline controversial. He did it, and I think he's going to benefit from it.
"I talked to Alex about it all the time. He's got to be his own man. You can't force a guy to deal with bullets when they are not used to having bullets shot over in a window. I grew up with bullets shot at me. It's a different thing, and I can understand it."
Sheffield fancied himself a guiding influence on Rodriguez in their three seasons together in New York, often pulling the All-Star aside to whisper in his ear to alternately commend and challenge.
Sheffield fought injuries last season and, limited to 39 games, eventually lost his starting role when the team acquired Bobby Abreu from Philadelphia on July 30. He hinted that he would accept some responsibility for Rodriguez's struggles in 2006.
"I wasn't there to stay in his ear," Sheffield said. "Even when he didn't want me in his ear, I'd make sure he was going to listen. Certain things have to be said. I knew when to approach Alex and when not to, when he's having his moments. I'd pull him to the side, say it, and keep walking."
Rodriguez said he appreciated Sheffield's contributions during their years as teammates.
"Sheff was always very good for me," Rodriguez said. "He's a good friend and a good teammate. I enjoyed having him. We're going to miss him."
Rodriguez added that, weeks later, he is satisfied with the outcome of the statements.
"It just felt good ending it," Rodriguez said.
The Yankees traded Sheffield on Nov. 10 to Detroit, where he is preparing for life as a designated hitter and a pursuit of the 45 home runs he needs to reach 500.
Though he is pleased to be reunited with manager Jim Leyland, one of his all-time favorites, Sheffield said he would miss a great deal about playing in New York. He said he hoped to receive a warm reception when the Tigers visit Yankee Stadium in August.
"Just thinking about it, man, I get chill-bumps," Sheffield said. "I'm going to miss that. I'm going to miss 50,000 people screaming and the stadium about to come down. It's the best atmosphere to play in, by far."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.