The Pirates will option Stratton to Triple-A Indianapolis on Thursday, Alex Stumpf of MLB.com reports.
After rupturing the patella tendon in his left knee in August, Stratton spent most of camp finishing up his rehab. He pitched in a Grapefruit League game Saturday, but he'll begin the season in Triple-A as he continues ramping up. Once the Pirates deem the right-hander ready for big-league action, he'll be a candidate to pitch in high-leverage situations.