Mario Manningham was the most-watched former Warren G. Harding High School player in college football last season. But Manningham left the University of Michigan after his junior season and is about to enter training camp with the Super Bowl-champion New York Giants. Now it’s time for another college junior from Warren to assume a high-profile position in the Big Ten Conference. Rocco Cironi won the starting left tackle spot at Michigan State. There may be no bigger key to the Spartans’ offense this fall than Cironi, a 6-foot-6, 306-pound lineman. He showed what he could do during the Spartans’ spring workouts. ‘‘Spring ball was very important to me to come out and let my teammates know I can play,’’ Cironi said. ‘‘I wanted to let them trust me and let my coaches know I can play, and that they shouldn’t have any worries.’’ Cironi will be blocking for running back Javon Ringer, who rushed for 1,447 yards and six touchdowns as a junior last season.