Already, Manning and the Colts struggled to punch the ball in the end zone with Harrison during a 22-20 victory (two of Indianapolis’ sub-25-yard field goals were against the Titans.)

This assumes that Harrison does not come back from his knee injury — a possibility, according to some reports. Or the knee bruise will be something that will inhibit Harrison even if he does come back, which could be as soon as this Sunday’s game at San Diego.

Either way, one of Manning’s most difficult tasks will be breaking his habit of looking toward Harrison. That’s a hard habit to break, considering all the extra hours over their careers the two have spent practicing together, and the fact that Harrison has led the Colts in either receptions or receiving yards (usually both) since Manning’s second year in the league, 1999.

Manning is going to have to learn to put more faith in Moorehead, Gonzalez, and other receivers such as Ben Utecht and Bryan Fletcher, while they will have to step up to earn that trust. (Gonzalez will have to wait to do so — according to NFL.com, he's out three to four weeks with a dislocated thumb that might also have a torn ligament). Those receivers are going to have to take advantage of the one-on-one coverage they will get while Wayne, Clark and Addai are blanketed, though even Clark might not play Sunday against San Diego — he has missed practice this week because of a concussion*.

That’s a very tall order, though. Can anybody outside northern California remember who Jerry Rice’s replacement was? It was J.J. Stokes, who was a certifiable bust. Not the encouraging word Manning would want to hear while dealing with the possible loss of Harrison.

Harrison says he believes he can come back, and he thought he was ready for the New England game. Coach Tony Dungy held Harrison out because he didn’t want to risk long-term damage to the receiver’s knee. Dungy isn’t going to have that luxury come playoff time. Not if he wants his Colts to repeat as Super Bowl champions.

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