The Giants placed Jackson (elbow) on the 15-day injured list Thursday.
Jackson is just under a year removed from getting Tommy John surgery, and though he has since resumed throwing bullpen sessions and could soon be ready to face hitters, he's most likely at least a month away from heading out on what will presumably be a prolonged rehab assignment. Whenever the Giants determine Jackson is ready to return from the IL, he'll likely be ticketed for a middle-innings role, at least early on.