SAN FRANCISCO — Randy Johnson has never had a hurt shoulder among his long list of injuries, so it's hard for the Big Unit to predict when he might be back on the mound.

He hinted today it could take longer than a stint on the 15-day disabled list for his strained left shoulder to recover.

"As far as the time frame, everything's kind of 4-to-6 to 6-to-8 (weeks)," the 45-year-old said in his first extensive interview since the injury Sunday and then going on the DL on Monday. "What I've learned in this business, having four knee surgeries and three back surgeries, is you want to have a time frame. A doctor can't give you one, because there's intangibles that come into play when you're talking about the body healing."

An MRI on Johnson's shoulder Monday revealed inflammation and a strain. The five-time Cy Young Award winner and 10-time All-Star selection is 8-6 with a 4.81 ERA in 17 starts this season, his first with San Francisco.

Johnson, who last month became the 24th player in major league history to reach 300 wins, felt something in his arm on a swing during his start against Houston on Sunday but initially tried to pitch through it. He left the game after committing a throwing error in the top of the fourth.

At the time, he snipped: "I'm going to make this short. Right now it's a strain and I'm going for an MRI tomorrow. That's all I'm going to say."

On Tuesday, he was clearly still frustrated in his tone but had come to grips with another trip to the DL — the 10th in his 22-year big league career.

"It's always good to kind of let the dust settle," Johnson said. "I'm letting my shoulder heal. I think nobody would like it to heal faster than I. You kind of have to let it run its course. I'll continue to get treatment from the trainer and hopefully everything moves in a positive direction. If anything, it couldn't have happened at a better time right before the All-Star break. It doesn't make me feel any better."

He initially felt the discomfort in his arm on a swing during batting practice several days ago, then again when he threw a curveball in the game. In hindsight, he said he wishes he wouldn't have swung.

Johnson said it's the first time in his career he's been removed from a start by an athletic trainer coming to the mound.

"My velocity dropped. I was throwing BP out there," he said.

Manager Bruce Bochy said he hoped Johnson would only have to miss two starts. He can't map out his rotation for after the All-Star break at this time considering Johnson's questionable status along with the fact starters Matt Cain and Tim Lincecum are headed to St. Louis for the Midsummer Classic.

"Randy's presence and his way of sitting down with the guys has been a tremendous help to these young arms," Bochy said.