SARASOTA, Fla. -- A tweak in Koji Uehara's left hamstring could mean a change of plans in the Orioles' Opening Day bullpen.

Uehara entered Thursday's game with four scoreless spring innings before he felt something in his left leg on an 0-2 pitch to Toronto's leadoff man Jose Bautista. The 34-year-old was diagnosed with a left hamstring strain; an injury that would be minor for any other player and, perhaps, any other leg. But Uehara has a long history of left hamstring problems -- dating back to his days in Japan -- and Baltimore shut him down for good last season in mid-September.

"I am not led to believe that it is anything that is going to be ongoing," president of baseball operations Andy MacPhail said. "But we don't know. But right now, it is going to be day-to-day."

Manager Dave Trembley echoed MacPhail's sentiment, saying he's not concerned about the righty's status for Opening Day on April 6.

"I feel very confident that he'll be ready for the season," Trembley said. "I've been led to believe that it's a day-to-day thing. If it gets to a point two or three days before camp ends, then I'd have some reason to be alarmed. But I'm not now."

Uehara said the injury is not in the same spot that plagued him last season, but obviously, it is still in the same general region. He was scheduled to play light catch on Saturday, but he opted instead to lift weights, with the possibility of tossing on Sunday.

"I'm always concerned," Uehara said, when asked if he was worried about the extent of the injury.

There is no timetable for Uehara to get back on the mound, and with 2 1/2 weeks left until the Orioles open the season, there is a chance Trembley will have to explore other avenues.

"We do have options," Trembley said. "My first option would be to know [Uehara is] going to be in that bullpen, because he's been very good this spring."

Fortunately for Trembley, those other options haven't been too bad, either.

Prior to Uehara's injury, it was widely assumed that there were three bullpen spots up for grabs this spring: two right-handed arms and the role of a left-handed specialist, which is a competition mainly between southpaws Will Ohman and Alberto Castillo. If Uehara isn't ready to start the season, it would open up another right-handed spot for Matt Albers, Kam Mickolio, Cla Meredith and Dennis Sarfate, among others.

Of the quartet, Meredith's numbers have him in the best position to make the team. The righty sidearmer has thrown six scoreless innings and hadn't allowed a hit until yielding a pair of singles Saturday.

"The arms race that we have here is a good thing," Meredith said. "There's a lot of legalities that kind of go into different decision-making, but the bottom line is, guys go out and perform. And if I get people out, people got to take notice. You just hope that you do your job and hope you get an opportunity to play in the big leagues."

Albers and Mickolio both pitched in Saturday's 5-2 win over the Pirates, with Mickolio fanning two and allowing one walk and one hit over 1 1/3 innings. The big right-hander drew raves from Trembley earlier this spring, with the Orioles' manager even going as far as to say one of the bullpen spots is Mickolio's to lose.

In six games, Mickolio has a 2.45 ERA, giving up two runs on six hits and five walks over 7 1/3 innings.

Albers also tossed a scoreless four-out outing on Saturday and has a 2.08 ERA over 8 2/3 innings, which is the highest inning total among any non-starter. Sarfate has struggled the most, yielding three runs on six hits with two walks over six innings. In five games, he has a 4.50 ERA.