Board Thread:Questions and Answers/@comment-27210738-20151113205526/@comment-28044177-20160602154703

He didn't discarded it. That's what Aizen thought because he couldn't sense Ichigo's Reiatsu. But we find out that it was because Ichigo was in an even higher dimension of power than Aizen, and not even he could sense Ichigo's Reiatsu.