Manager Bob Melvin announced Friday that Randy Johnson will not make his scheduled start today against the Orioles and has been placed on the disabled list because of glute tightness. Melvin said Johnson began feeling it while playing catch in Phoenix this week, although he also said that the injury probably is related to Johnson's sciatic nerve. During spring training, Johnson had to delay his throwing schedule a few days after he felt irritation in the nerve. Melvin said Johnson underwent an MRI exam Friday. The club still was waiting for the team doctors to review the results but acted swiftly in placing Johnson on the DL. "We are going to err on the side of caution," Melvin said. "I said that from Day 1. That's how we're going to handle it. We're not going to run him out there in a situation where it could get worse."