FORT MYERS, Fla. -- Boston Red Sox closer Koji Uehara threw 30 pitches in a bullpen session Monday, and the news is not good: He felt the same sensation in his left hamstring that has prevented him from taking the mound since March 14.

Even before that on Monday, manager John Farrell said, "I don't think there's anything to suggest that come next Monday, he's in our bullpen."

That means Uehara likely will start the season on the 15-day disabled list.

"I think I'm going to start on the DL just because I haven't had the games in," Uehara said through interpreter C.J. Matsumoto. "If that is the case, if I start on the DL, it will certainly be a disappointment."

Uehara said he knew from the time he first injured the hamstring that it was going to be a slow process, so he's not too disappointed about what has transpired since.

"I don't know when I'll be back," he said. "It's a day-to-day process. I have to do what I have to do to get ready."

Asked if his experience had taught him not to rush the recovery, he said, "Absolutely."

Uehara was on the DL with a left hamstring strain to start the 2010 season, returning on May 5, and went on the DL 15 days later with a right forearm strain. In 2012, he went on the DL on June 10 with a right latissimus strain, and while returning from the injury in mid-July, he re-aggravated it and ended up being on the DL until Aug. 25.

Farrell said he isn't sure whether he will start the season with a seven- or eight-man bullpen.

"I don't have seven names to give you right now," he said. "We've still got some things to determine. How we're going to determine the rotation, whether we go with an additional left-hander or right-hander, what the ramifications of Koji coming out of the mix for the short run. Does that likely move Edward (Mujica) back into the closing role?

"I do know this: We're at a point in camp when guys are throwing the ball as expected, and that includes Robbie Ross. That's Matt Barnes. Brandon Workman's last time out was encouraging, so as we get to the final week of camp here, the guys we felt would be in contention for spots are moving in the right direction."