The Cubs had feared something worse.
"I'm very pleased," Cubs team trainer Mark O'Neal said of the initial report. "There's bad news, extremely bad news, that could come out of it.
"Right now, if this is a posterior shoulder strain, we're going to deal with it like you would a hamstring strain. Unfortunately, it's in the shoulder. So yes, for us, it's pretty good news," he said.
Prior visited Dr. Lewis Yocum in Los Angeles on Wednesday, a day after feeling pain in his right shoulder before he could take the mound for a bullpen session.
Prior was scheduled to have an MRI exam in Los Angeles on Thursday to determine whether his shoulder has suffered more extensive damage.
Yocum and the Cubs medical staff will meet in Arizona on Saturday to discuss Prior's status and determine a course of action.
Prior has not thrown in an exhibition game this spring, but the Cubs have insisted there has been nothing wrong with him and that the shoulder problem came up just this week.
The team said it was easing Prior into action because elbow problems limited him to just one exhibition start over the previous two springs.
Prior was 11-7 with a 3.67 ERA in 27 starts last season. He began the 2005 season on the disabled list with inflammation in his right elbow, but he missed just his first start. He later missed almost one month after being hit on the right elbow by a line drive in late May.
Prior has a lifetime record of 41-23 with a 3.24 ERA.