"It seems like he's still getting some impingement in his shoulder; we're going to have an MRI and take a look at it," manager Brad Mills said.
Arias, 27, came to camp with a clean bill of health but experienced some discomfort on one of the first days of throwing in the bullpen.
"He's going to be behind, there's no doubt," Mills said. "This latest incident that has come up is really going to put him back there. The important thing is to get him healthy and strong and going again. In the long run, we hope that's going to happen for him.
"We haven't seen him pitch now in quite a while. We need to get him back and healthy and strong for his sake and his career, and if he can help benefit us, we're all better off."