This injury of his might prove to be useful in the long run. 2 seasons ago he started bad and then he was benched. It resulted with an explosion in the second part of the season. Last year he had a shorter vacation due to the Euros and he was overplayed due to Trezeguet's and later Amauri's injury. In the later part of the season it was obvious that he's tired.
Now he had a completely free summer and he's starting the season much later than the rest. It will probably take him some time to get into shape and start performing, but he'll be well rested and he'll hit form right at the time when the other teams' fitness will become worse.
Not to mention the motivation he'll have in order to win a world cup spot.
Another injury aside, I can easily see Del Piero shining in the second part of the season. Hopefully we'll make it through the CL group. If we do, then we'll have a deadly weapon in February when the knock-outs start.