Trammell was diagnosed with a right calf strain Saturday, Brian McTaggart of MLB.com reports.
Trammell suffered the injury Friday while running the bases and is set to be out for a while, though the Astros didn't specify exactly how long that will be. The 27-year-old outfielder is fighting for a spot on the Astros' roster after being traded from New York in November, but his latest injury doesn't help his chances.