Stewart (hamstring) will begin a rehab assignment with Double-A Altoona on Thursday, Rob Biertempfel of the Pittsburgh Tribune-Review reports. It's not clear how many rehab games Stewart will need before being activated from the disabled list, but he should be ready for big league action at some point in the next week or two. When he is ready to go, Stewart will likely replace Tony Sanchez as the backup catcher behind Francisco Cervelli.