The tear was diagnosed after an MRI test, team doctor Bruce Thomas said Saturday.
Lawrence came into training camp hoping to make the starting rotation. Now it's likely he won't return until midseason or later,
"Injuries have never been an issue with me," Lawrence said.
"I never felt any pain until the first day I showed up here."
Lawrence started throwing the day before workouts officially began. He said he felt good, but something went wrong after his first bullpen session.
"I threw and it was hurting. I actually felt decent, but then
the next day it wasn't there," he said.
The MRI test showed a split in his labrum, "a small
washer-shaped shock absorber in the shoulder" Thomas said.
The Nationals acquired Lawrence from the San Diego Padres for third baseman Vinny Castilla at the end of last season. Lawrence went 7-15 with a 4.83 ERA in 33 starts for the Padres in 2005. He struck out 109 batters and walked 57 in 195 2/3 innings.
The 29-year-old right-hander is 49-61 with a 4.10 ERA in his five-year major league career.