BALTIMORE -- Daisuke Matsuzaka has been placed back on the disabled list, retroactive to Saturday, after experiencing a strained right trapezius muscle.
Matsuzaka must spend a minimum of seven days on the DL before resuming another rehab assignment in the minors.
The Red Sox scratched him from a scheduled rehab start Tuesday night and gave him an injection to help the muscle over the weekend in Philadelphia.
"The same area flared up maybe three weeks ago," said Matsuzaka through an interpreter. "It was the same symptoms. It restricts my movement when I throw. At this point, that's why I got the shot and hopefully, it gets better from here.
"My rehab so far (from Tommy John surgery) has been going really well. It's a setback and it is a little bit disappointing. But I'm hoping the shot takes care of it and we can just continue my rehab from there."
Matsuzaka said he already feels the effect of the shot and is hopeful of throwing a bullpen later this week.
"We expect this issue will be resolved,'' said GM Ben Cherington, "because it's been resolved in the past. When that happens, we'll get him ramped back up and (sent out on another rehab).''
But Matsuzaka emphasized that he doesn't want to rush his return and compromise his health.
"I don't want to, and I don't think I can, pitch until I'm 100 percent physically and mentally,'' he said. "That's the type of patience I need to continue working with until I make a comeback."