Manager Don Wakamatsu said Friday that the team's medical staff decided the 31-year-old left-hander will do no more throwing until at least Wednesday.
Asked if there was any way around Lee beginning the season on the 15-day disabled list, Wakamatsu said, "I think we're just going to wait and see how he responds Wednesday."
Seattle's prized winter acquisition from Philadelphia felt pain in his lower right abdomen for the second time in three days Thursday after throwing lightly on flat ground for a few minutes. He first injured it March 15 in a collision with Arizona's Chris Snyder while Lee was backing up the plate on a scoring play.
Even if he responds well to five days of rest, he is unlikely to be ready to pitch before the Mariners break camp Thursday. The Mariners have final exhibition games in Albuquerque on April 2 and 3, and at San Francisco on April 4. The season begins April 5 at Oakland.
Lee was supposed to start April 6 against the Athletics, in the rotation spot behind co-ace Felix Hernandez — pending Lee's appeal of a five-game suspension for zipping a fastball over Snyder's head after the collision in that spring game. That appeal will be heard Monday in a conference call from Phoenix with the league.
Lee has not been on a mound since stopping a bullpen session because of the pain in his abdomen on March 18. He would need a couple of bullpen sessions before testing the muscle in a game. The Mariners will likely have started the season by then.
This is his third strained abdominal muscle since 2003. Wakamatsu noted the other two injuries, which also happened in spring training when he was with Cleveland, had Lee out at least six weeks.
The Mariners are treating Lee with platelet-rich plasma injection therapy. The first session came last week. In the relatively new procedure, a tube of a patient's blood is taken and put in a centrifuge and spun, producing concentrated platelets. Those contain growth factors that accelerate tissue repair and regeneration. The platelets are then injected into the injury site.
The treatment gained notice in 2008 after Pittsburgh receiver Hines Ward used it on his sprained right knee to help him play in the Steelers' Super Bowl win over Arizona.
Pitcher Takashi Saito avoided surgery on a partially torn ligament in his throwing elbow by using platelet-rich plasma injection therapy during the 2008 season. He was able to come back in time to pitch late in the Los Angeles Dodgers' playoff race.
"I'm fairly new to this platelet-injection stuff. It's pretty wild to me," Wakamatsu said. "It looks like there's been great results with it. We're trying to be optimistic."