Freshman compete for spot before Lewis expected back to start Big Ten play.

Illinois redshirt freshman offensive tackle Michael Heitz didn't get much time to sit and watch, but he likes it that way.

The Table Grove VIT High School graduate and former star for the South Fulton co-op program is competing with classmate Simon Cvijanovic for the starting spot on the strong side while the Illini await the return of junior Corey Lewis, a former starter who reinjured his knee in the offseason.   Called into the football office last spring, Heitz and Cvijanovic quickly moved up the depth chart.   "I heard from other teammates that Corey got hurt,'' Heitz said. "Then the coaches called me and Simon. They said we had a teammate get hurt, so it's time for us to step up. We're not freshmen any more. The team needs me. I'd much rather be playing the whole time.''   The day-to-day battle likely won't be decided until later in the month, because both players have their individual strengths. Lewis might return by the start of the Big Ten Conference season, but the Illini also need a backup at weak-side tackle. The Illini flip the lines, allowing the strong side to play next to the tight end.   "It's right out here where we're going to prove it,'' said Heitz, standing next to the Camp Rantoul practice field. "If I don't come out here and compete for the spot, it's going to be his.''   Heitz is a 6-foot-5, 295-pounder who earned all-area by the Peoria Journal Star after leading South Fulton to the Class 1A quarterfinals as a senior. He started all 41 varsity games during his high school career. First noticed by Western Illinois, then Illinois State and Northern Illinois, Heitz saw his reputation grow after attending combines in Indianapolis, Oklahoma City and Orlando, Fla., prior to his senior year of high school.   He chose Illinois over Wisconsin, before the other offers started piling up.   Cvijanovic is a 6-5, 285-pounder from Cleveland Benedictine who chose the Illini over Toledo, Ohio and Bowling Green. When the Illini complete the first team scrimmage Saturday (6:30 p.m., Rantoul High School), the coaches may adjust the depth chart, perhaps giving one player more snaps with the first team.   "Michael is a big, physical kid,'' said offensive line coach Joe Gilbert. "In the run game, he gives us a little more pop. Simon is probably a little bit better in pass protection, as far as knee bend, hand placement and adjustment.''   The massive Heitz is still trying to keep his pads lower.   "Overall, my tendency is to stay high,'' Heitz said. "My big thing is staying long on everything I do. As practice goes, I tend to stand up. My legs get tired.''   The rest of the line is filled with returning starters -- the first-stringers at the other four interior positions have 68 career starts. "All five have to work together,'' Gilbert said. "If you have one missed assignment or one guy who doesn't hold up, it doesn't matter about the other four. Assignment wise, it helps Michael and Simon are both very smart. It's not an issue of assignment. It's who is better with technique and who is better at getting the job done.''   By flipping the line, "it's easier to protect them at times and help them out,'' offensive coordinator Paul Petrino said.   The Illini will be patient with Lewis, Gilbert said.   "We have to play it by ear,'' Gilbert said. "I've coached the O line long enough to know if we've got a group of guys playing well, we're going to go with that group. Corey will work in. He's a talented kid. We want to be very smart and try not to bring him back too fast.''