Oliver suffered a "significant" hamstring injury at practice Thursday, Michael DiRocco of ESPN.com reports.
Coach Doug Marrone was unable to offer a recovery timetable for Oliver, but the coach classifying the injury as "significant" indicates Oliver could be facing a multi-week absence, at least. The rookie third-round pick entered training camp looking to supplant free-agent acquisition Geoff Swaim from the starting role, but that will be a difficult proposition if he ends up sidelined for a chunk of the preseason.