Grady Jackson, the 350-pound defensive tackle, who was signed to shore up the defensive line, attended mandatory minicamp last week, but didn’t practice. He’s coming off knee surgery in mid-February and the Lions want to err on the side of caution before letting him on the field.
 Jackson said there’s no question he’ll be ready to play by the start of the season, but he could face a possible suspension for violating the NFL’s drug policy last season as one of several players who tested positive for a banned diuretic.
  The Lions are aware that he could be suspended.
  “We definitely have that in mind with it, for sure,’’ Schwartz said.
  Jackson said he’s been given no timeline on the issue by the league.
 “I don’t know too much about no suspension right now. Nobody’s saying nothing. I have to wait until it comes,’’ Jackson said.
— PAULA PASCHE