Brick under fireplace

My friend is renovating their house and their contractor told them they need to fix the brick arch below the parlor floor fireplace. He said he could parge it or install some framing and plywood. What have you seen done before?
I have adamantly advised reaching out the eor. [IMG_4899](//muut.com/u/brownstoner/s3/:brownstoner:ZP8E:img_4899.jpg.jpg)