General manager Jon Daniels said Wednesday that Harrison has been diagnosed with significant nerve irritation in his vertebrae. He will have an injection Friday in an attempt to alleviate the symptoms before considering other options, including surgery.
Harrison, who made only two starts last season before two operations on a herniated disk in his lower back, came out in the second inning of his start Tuesday night at Houston.
Perez has a partial tear of his ulnar collateral ligament in his left elbow. He could have an injection and rehab that could keep him out three months, or possibly have Tommy John surgery.