The details that Posada and the Yankees agree upon are that the 39-year-old went to manager Joe Girardi approximately one hour before Saturday's scheduled first pitch and asked to be taken out of the lineup against the Red Sox.
"I told them I couldn't play today and I needed time to clear my head. That was it," Posada said. "My back stiffened up a little bit. I was taking a lot of ground balls at first base and worked out and wasn't 100 percent."
The slumping Posada insisted that it had nothing to do with being demoted to the No. 9 slot. He added that he saw a chiropractor -- but not the training staff -- before also saying that he needed a mental health day.
"It was a little bit of both," Posada said. "I can't lie to you. I was honest with you. I wasn't able to play. I took that and used it as an excuse of coming out of the game."
Girardi and general manager Brian Cashman both said that an injury was not mentioned during the conversation in the clubhouse, and Posada later confirmed that he did not bring it up.
"The conversation was really short," Girardi said. "Jorgie came into my office and said that he needed a day and couldn't DH today. That was basically the extent of the conversation."
Asked if he had mentioned the back issue to either Girardi or Cashman, Posada replied, "No, I did not. I felt that I wasn't able to play today."
A reporter then asked Posada why he wouldn't tell his manager and general manager, to which he responded, "Because it wasn't a serious issue."
The Yankees used Andruw Jones instead as the designated hitter in their 6-0 loss to the Red Sox, a game that Posada watched from the bench while wearing a hooded sweatshirt.
Posada said that he did not talk to Girardi at any point during the game; Girardi was ejected in the seventh inning by home-plate umpire Mike Winters for arguing balls and strikes.
"This is a situation, obviously, that we'll take care of," Girardi said. "Players go through difficult times in this game. We all do. Sometimes we need days to clear our head and take a deep breath.
"I've been there. I've been through struggles, and this season has been a struggle for Jorgie. It has been. He has tried to fight through it, and today he just felt like he needed a day."
Posada said he was irked that Cashman had made an announcement of his situation during the game, although it is customary for the club to provide a reason for late lineup changes when they involve injuries.
In this case, Cashman first spoke on the air with the FOX broadcast and then met with a gathering of reporters during the third inning on Yankee Stadium's press level.
Cashman largely declined comment except to say that he had spoken with Posada and there was no injury to discuss.
"I don't know why he made a statement during the game," Posada said. "In the middle of the game, I don't understand that. That's the way he works now."
During the game, Posada's wife, Laura, stated that her husband indeed had been unable to play because of injury.
"Jorge loves being a Yankee [more than] anything," she wrote on Twitter. "He's trying his best to help his team win. Today, due to back stiffness he wasn't able to do that."
Girardi had decided to drop Posada to ninth after a poor start to his 2011 season. In 125 plate appearances, Posada has a .167 average with a .272 on-base percentage.
"His struggles have been tough on him," Girardi said. "As I've said, I've been through struggles that have seemed extremely difficult in my career.
"Jorgie has always been a guy that has worn his emotion on his sleeve. He plays with a lot of passion and a lot of fire. Today he just felt like he needed a day."
Across the field in the Red Sox's clubhouse, David Ortiz expressed sympathy for Posada's situation.
"You're talking about a guy that played a position his whole career," Ortiz said. "Now, I got used to this because I got no choice, but I can imagine how hard it has to be for him. This is a guy that is a good hitter. I don't care what anybody says."
Posada had seemed in calm spirits discussing the lineup change with reporters before 4 p.m. ET, acknowledging responsibility for his unimpressive stats and saying that the only way he would move up in the lineup is to hit.
"I talked to you guys before the game and I was clear with that. I put myself in that situation," said Posada, who hasn't hit ninth since May 14, 1999.
"I haven't hit the way I wanted to. I talked to you guys before the game, and you know what I was feeling. I was looking forward to playing the game."
In his first year as a full-time DH, the switch-hitting Posada has 18 hits, but six of them are home runs. All 18 hits have come against right-handed pitching. He is 0-for-24 against lefties.
Even if he arrives at Yankee Stadium on Sunday and proclaims himself healthy, there are no guarantees that Posada would immediately return to the lineup.
The Yankees' next two games are against left-handed pitching -- Boston's Jon Lester and Tampa Bay's David Price.
"It's been tough. It's all about the team," Posada said. "I think we have to talk about the game today. We need to get going."