The Mariners' corresponding move before Friday night's game against the Rangers was optioning reliever Shawn Kelly to Triple-A Tacoma.
Lee has been out since he strained his abdomen during a spring training game on March 15.
The 2008 AL Cy Young Award winner says he's been pain-free for weeks. But Seattle's prized winter acquisition from Philadelphia dutifully followed the team's cautious rehabilitation plan for his third strained abdomen since 2003.
The 26-year-old Kelley has pitched in six games this season, with a win and a 2.57 ERA in seven innings.