Someone was making a dough for matzah and a piece of chita (chometz) fell into it. L’maseh before Pesach this is buttel. However there is a shailo of “chozer v’nirah”. In a case of lach b’lach there is no din of chozer v’nirah. In the case of yevash b’yevash there is a din of chozer v’nirah. Is the piece of chita with the dough mixed together a case of lach b’lach or yavesh b’yavesh.
This is a delicate question.
Having investigated the matter a number of years ago, the concensus of poskim for dough that falls into dough is that it is considered lach be-lach, and therefore battel.
However, in your case a solid piece of chametz fell into the dough, and it is not a question of dough falling into dough.
Depending on the type of chametz that fell in, there is possibly room to say that it will crumble up, and become a part of the dough. However, for most solid types of chametz, I don’t see room to be lenient in this matter.