The injury is not considered serious. An MRI showed inflammation in the knee.
As a precaution, Strasburg is scheduled to fly to Los Angeles on Friday to be examined by Dr. Lewis Yocum.
Strasburg, who was the first overall pick in the 2009 First-Year Player Draft, made five starts, going 4-1 with a 4.26 ERA. He struck out 26 batters in 19 innings for the Desert Dogs.
It marks the second time Strasburg was injured during the AFL season. Previously, a neck injury forced him to miss a start.
Strasburg reportedly hurt his left knee while shagging fly balls.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.