"Even before I went up on the mound, I felt that things were a little bit off in the bullpen," Matsuzaka said through interpreter Masa Hoshino. "I wouldn't go so far as to call it discomfort, but I wasn't at my best, even before going into the game. After pitching the third inning, I definitely felt that there was something wrong. At that point, I had a conversation with the coaching staff. I did go back out there for the fourth and gave it a try. But I thought it was best to stop after that."
The Red Sox are describing the injury as right shoulder fatigue, and, at this point, it's uncertain whether Matsuzaka will be able to make his next scheduled start in Baltimore on Monday night.
"He felt some, I guess fatigue is the right word," said Red Sox manager Terry Francona. "We're not going to run somebody out there when we think there's a chance [of making things worse]. It's too long of a season. I don't think he really wanted to give the ball up. But again, it's a long year. Just doesn't make sense to me to do something like that."
Francona had made up his mind after four innings that Matsuzaka was done for the night. But when Boston's top of the fifth ended abruptly on a double-play ball off the bat of Julio Lugo, Matsuzaka snuck back to the mound before Francona had a chance to tell him he was through.
It didn't much matter. Matsuzaka threw a couple of half-hearted warmup tosses and knew that it didn't make sense to go any further.
"At that point, I felt if I had to keep pitching, I would be able to do, but I got out there and got my warmup pitches in and things just didn't feel right," Matsuzaka said. "Since, as I've already mentioned, this is something I have experienced in the past, I'm not overly concerned about the situation right now."
Matsuzaka recalls having a similar feeling early in his pro career in Japan.
"I had a similar experience probably in my second or third year of my professional career, where before the game, I felt that things weren't 100 percent, and I had a similar feeling, so I had a conversation with the coaching staff at the time," Matsuzaka said. "I think at that time, I ended up starting the game and went deep into the game. Today, with so much season left and such a long way to go in this long season, I thought it would be best to come out of the game at that point."
In this abbreviated start, Matsuzaka gave up four hits and three runs (two earned) over four innings, walking none and striking out two. He took a no decision and remains unbeaten (8-0) on the season, with a 2.53 ERA.
The Red Sox lost the game, 4-3.
Matsuzaka will be examined more on Wednesday. Will he pitch in Baltimore?
"It's hard to say until we're able to assess the situation again tomorrow," Matsuzaka, said. "The team trainers took a look at it, but it's hard to say without giving it a little more time, so we're going to check it out again tomorrow."
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.