MIAMI BEACH, Fla. -- The worst performances of the season for Indianapolis Colts quarterback Peyton Manning came -- take your pick -- Sept. 24 against Jacksonville, when his percentage of completions dipped to 45.2, or Oct. 8 against Tennessee, when his total yardage was a season-low 166. The worst performance of the season for Chicago Bears quarterback Rex Grossman came, uh, well we're going to have to sit down and figure this out.

Was it Oct. 16 against Arizona, when he completed 14 of 37 passes for 144 yards, threw four interceptions and had a passer rating of 10.2, which is about 65 points below average?

Or was it Dec. 3 against Minnesota, when he completed 6 of 19 passes for 34 yards -- yes, that's right, less than 2 yards per pass -- threw three interceptions and had a passer rating of 1.3

Actually, it was neither of those. The game where Grossman truly stunk out the joint was Dec. 31 against Green Bay, in what was supposed to be a tune-up for the playoffs. In that game, he threw 12 times and completed two for 33 yards. He threw three interceptions. He had a passer rating of 0.0.

Of course, he had an excuse. Afterward, he acknowledged he didn't care about that game.

So the question to be asked with Super Bowl XLI about 48 hours away is : Which Rex Grossman will show up to compete against Manning and the Colts?

If it's the awful Grossman, the Bears have no chance. If it's the reasonably competent Grossman, the Bears are capable of an upset.

Grossman is well aware of his up-and-down performances.

"I've had 18 games," he said at a interview session. "There are 12 games that I'm extremely proud of and six games that are bad. In my first full season, I think that's pretty good. I definitely want to eliminate some of the bad games and be consistent."

Ineptitude at quarterback is nothing new for the Bears. Although they are one of the NFL's legendary franchises, they did not build their reputation on the strength of their quarterback play.

Sid Luckman is the Bears' all-time passing leader, having thrown for more than 14,000 yards. Luckman is in the Hall of Fame, but if you haven't heard of him, it's understandable. He retired in 1950. Which means the record he established when passing, which then was comparatively rare, has stood for 56 years.

By comparison, the Colts' franchise, about 20 years younger than the Bears, has three quarterbacks, Manning, Johnny Unitas and Bert Jones, who have thrown for more than 14,000 yards.

Bears quarterbacks have had only three 3,000-yard seasons. By comparison, the Colts have had 14.

The Bears' quarterback situation has been so shaky that when Grossman opened the 2004 regular season, he was the seventh starter in seven years. The Bears' passing leaders from 2002-05 were these legends: Jim Miller, Kordell Stewart, Chad Hutchinson and Kyle Orton.

Grossman, who had a great college career at Florida, knew he wasn't exactly walking into a path blazed by immortals.

"A lot was said when I was drafted about the struggles they've had at quarterback. I know Jim Miller played well for a while, and Erik Kramer had a couple of really good seasons, but they haven't had a consistent quarterback really for a long period of time, since Sid Luckman."

When it's only the shadow of Miller and Kramer looming, expectations aren't pegged too high.

And the Bears like it that way. They don't expect Manningesque performances from Grossman, but nor do they want Kordellian ones. They prefer he be a contributor to their offense, not the focal point. Grossman needs to be himself, which means being the good Grossman, not the awful one that has shown up too often.

Grossman has been fine in the postseason. In the Bears' overtime victory against Seattle, he completed 21 of 38 for 282 yards. In the NFC championship game against New Orleans he was 11 for 26 for 144 yards. He has thrown one interception in the playoffs.

Offensive coordinator Ron Turner will be cautious Sunday with Grossman.

"We run our offense," he said. "Within our system, within our offense, we are always going to take shots. We're always going to try to get some big plays. You have to be able to run the ball, but you have to score points, and to score points, you have to get some big plays in there. We are going to give Rex those opportunities. We're going to continue to do that, and he has to continue to be smart."

If Grossman turns stupid, if he plays one of his bad games, it could get embarrassing -- for him, the Bears and the NFL.