NEW YORK -- Yankees lefty Randy Johnson has a herniated disc in his lower back, an injury that could prevent him from pitching in the playoffs next week.
The injury was discovered during an MRI exam Thursday. After being examined by team physician Dr. Stuart Hershon and back specialist Dr. Paul Kuflick, Johnson received an epidural injection Friday.
"Hopefully that will ease the discomfort," New York manager Joe Torre said before the Yankees beat the Blue Jays 7-2 on Friday. "If it doesn't ease the discomfort, I'm not sure he's going to be able to pitch. But we don't expect that to be the case."
New York's win, combined with losses by Detroit and Minnesota, assured the Yankees home-field advantage throughout the postseason.
Torre's announcement came one day after the crosstown Mets said Pedro Martinez will miss the postseason because of a torn tendon in his left calf muscle.
Johnson, who turned 43 on Sept. 10, is expected to play catch Saturday and throw a side session Sunday at Yankee Stadium.
The Yankees wouldn't specify which disc is herniated but said it's not the one that caused Johnson to have back surgery in 1996.
Johnson has a 7.64 ERA over his last three starts, giving up five runs each outing and failing to last longer than six innings. He is 17-11 this season with a career-high 5.00 ERA.
"If he says he's ready to go or will be ready to go on Friday, we'll write him in. If things change, then we'll do something else," Torre said. "I certainly want Randy Johnson, bad back and all. His capabilities are very, very high. He's pitched for as long as he's pitched, and we know darn well he wasn't 100 percent every single step along the way."
If after watching the weekend sessions the Yankees don't think Johnson can pitch next Friday, Torre said he probably would omit the Big Unit from his first-round roster. If that happens, the Yankees would use Jaret Wright and Corey Lidle in Game 3 and, if necessary, Game 4.
General manager Brian Cashman said the disc is causing Johnson more tightness than pain and said he remained "cautiously optimistic."
"We hope to have him. I know he's intent to do everything he possibly can to be a strong and effective starter. So we'll see," Cashman said. "I think any scenarios are open. I think it's possible he goes the whole way [through the postseason]. It's possible he doesn't go at all. It's possible he goes partial. I think anything's possible on this one right now."
Johnson has been bothered by back spasms over his last few starts -- beginning a day after his birthday -- but didn't tell the team until after he allowed five runs and seven hits over six innings in an 8-0 loss last weekend at Tampa Bay. The Yankees then decided he would skip his final regular-season start.
"You don't know what you're going to get when he pitches," Torre said earlier this week. "The one thing I'm hoping for is that he feels better, and then we'll deal with the command at that time. But you can't have both. You can't have him stay sharp and throw and be able to rest something."
Johnson missed over four months of the 1996 season with a herniated disc in his lower back that required surgery. Torre and Cashman said they were unsure if this injury would also require surgery during the offseason.