The 2008 AL Cy Young Award winner said that the injury felt a bit better after five minutes of light throwing in the outfield grass of a side field.
Lee thought he would continue to throw off flat ground every other day for now but added he doesn't know for sure the team's plan for him beyond Thursday.
Each day he's not on a mound increases the likelihood Seattle's prized winter acquisition will be on the disabled list when the season begins April 5.
On Tuesday, Mariners manager Don Wakamatsu acknowledged it would be tough for Lee to be ready when the season begins given the team will be in camp for only another week.
This is Lee's third abdominal strain in seven years. The previous two, in 2007 and '03, had him on the DL to begin those seasons for more than a month each time.
Jason Vargas, a former Marlin and Met who had elbow and hip surgeries in 2007 and '08, has been the only consistently effective starter behind Hernandez.
Even if he suddenly healed, Lee may not be available to begin the season on time, anyway. He has a hearing on Monday through a teleconference from Phoenix with the league on his appeal of a five-game suspension for zipping a fastball over the head of Snyder. He did that a couple innings after they got tangled up while Lee was backing up the plate on a scoring play.