How long do pre-chopped portobello mushrooms last in the refrigerator?
This is probably way too late, but for the benefit of others with the same question...
I have been taught, and my experiences verify, that fresh mushrooms of any sort should only be washed if absolutely necessary and if do so, to do it at the last possible moment. I just brush off any noticeable growing media and continue on. For Portobello mushrooms, I do this while cleaning out the "Gills" so it takes no extra time whatsoever.
That said, Pre-chopping / slicing, will reduce the shelf life over the long term, but for an overnight stay in the fridge it will not be a problem.
I would love to hear how you made out. Did you end up washing them? Your experience will also help others with the same question.