ST. PETERSBURG, Fla. - This is no way to start a new season. Brian Matusz left the ballpark to undergo an MRI on his back after experiencing pain while trying to throw. He's a candidate to join Justin Duchscherer on the disabled list and create a possible ripple effect in the rotation. No. 3 starter Chris Tillman could be bumped up a day and start tomorrow night, or the Orioles could bring up a pitcher from their minor league camp. Manager Buck Showalter indicated that the pain is to the left side of Matusz's middle back area. "I already told Joe (Maddon) over there that he's not going to start, so he knows," Showalter said. "We've got some options that we'll decide when we get the MRI back, that will kind of affect what direction we go, depending on the severity of the injury." Showalter eliminated Brad Bergesen has a candidate. Bergesen has been assigned to the bullpen and could make the April 10 start unless he's needed sooner. Tomorrow night is too soon. "He's only had two days off after throwing two innings," Showalter said. "Tillman's available to throw tomorrow." Asked about the difficulty in receiving this news on opening night, Showalter said, "I think because of the day and the stuff surrounding opening day, maybe, but to think that one of our pitchers wasn't going to have a physical problem...Obviously with Duke (Justin Duchscherer) and (Matusz), it makes it a little more challenging. A couple line drives off the biceps and forearm will do that for you. We've just had a little spurt here where some things have cropped up. "(Jake) Arrieta is not an option for any day here. He threw six innings (Wednesday), so we went ahead and gave him his work day. He's not an option Saturday or Sunday, so he'll pitch Monday back there." Matusz was fine physically until today. "Today was the first day he had this type of discomfort," Showalter said. "He had a thing like most pitchers where they have a little trouble getting loose and it goes away and it's not a problem. Just about everybody here has it in some point or fashion. But today when he went out to throw and make sure he was ready to go, he had some acute pain there, which wasn't good. He only threw two or three throws and then Mark (Connor) and them got him off the field and decided to take it to the next step."