Lee, who the Rangers acquired earlier this season from Seattle, threw a bullpen session on Sunday and his back loosened up. Lee only threw in the outfield on Saturday and reported some continued discomfort in the area of his back where he recently got a cortisone shot.
Rangers officials said Lee is capable of starting on Tuesday at Toronto, but they have opted to be conservative as Texas works to clinch the American League West title. It is unclear whether Lee's start will be simply pushed back a day or two or whether his turn in the rotation will be skipped.
Lee is 10-8 this season with a 3.37 earned run average, but is 2-5 with a 4.69 ERA since coming to the Rangers from the Mariners.