Roberts left Thursday's joint practice with the Steelers after suffering a knee injury during special-teams drills, Rick Stroud of the Tampa Bay Times reports.
Roberts was able to walk off the field under his own power, but Stroud relays that the safety's injury could be a serious one. Roberts signed with the Buccaneers as an undrafted free agent in May and has been competing for a depth secondary spot on the 53-man roster.