"It's tough," said Ellsbury. "You work so hard to come back from something and you have a little setback like this. I think I'll know a little bit more information [Thursday], once we get back up to Boston."
Ellsbury was on the disabled list from April 12 until Friday due to a contusion of his left chest, not to mention a hairline fracture in four ribs.
He only had normal soreness in his first three games back in the lineup, but felt some discomfort while taking batting practice before Tuesday's game. Ellsbury felt only minimal improvement Wednesday. He underwent X-rays and a CT scan on Tuesday, which didn't reveal any breaks.
Ellsbury will be examined by the team's medical staff, which has monitored the injury all along.
"Well, I felt pretty good during the game the last three games," Ellsbury said. "I had the scheduled day off [Tuesday]. I just did my normal routine. I was hitting, and it started barking on me. That's when I talked to the trainer and kind of let him know what was going on. Progressively after I was done hitting, it actually got a little worse."
Ellsbury felt better when he woke up Wednesday, but when he tried to test it at the ballpark, he could tell something was still amiss.
"It was kind of barking on me again," said Ellsbury. "We shut it down."
It is too early for Ellsbury or the Red Sox to know if he will need to return to the disabled list.
"I hope not," said manager Terry Francona. "I think before we say that, I'm not sure. I'd like to know what it is first. We're just kind of doing a lot of guessing. We'll take all the pictures that were taken [Tuesday] with us back to Boston. We'll have all the people that have already seen him kind of review everything. I don't know that anything really changes. We're certainly going to try to have everything checked out, but it's probably how he feels. If you feel something, we want to be careful. So that's kind of where we're at."