Locke said he felt "a little pull on his right side" while throwing a bullpen over the weekend. He finished the session, then sought out the team's training staff.
"I've seen people do oblique stuff before, where they're so bad they can't even take a breath," Locke said. "That's not the case with me. Very minor. Nothing hurts at all. Precautionary more than anything; take a few days then re-evaluate.
"It's funny," he said. "I was just out there throwing normal, everyday stuff. And one thing I've heard is that, in the oblique area, it's usually the throwing side of the pitcher [that gets affected]. It could have been [caused by] coming out of a turn quickly, or not having stretched out enough."
Whatever the cause, Locke hopes for and needs a quick recovery. He knows he has to pitch to earn back the starting job that was taken away from him in mid-September.
"What bugs me the most is not being able to throw [Wednesday]. But I'd rather not be able to throw now than be unable in April or in June," he said. "It is the beginning of March; the last thing I want to do is find a way to set me back further."
Locke will continue to receive treatment on Thursday, and held out the possibility of trying to throw from the mound on Friday.