The 26-year-old striker could be available for little more than £8million should the Eagles sign a replacement. Leicester's Kelechi Iheanacho was a target in the summer and could be available, with just over six months left on his deal.
Mateta is frustrated at not starting a Premier League match since October and making just 19 starts over two years.
Frankfurt are keen to boost their attack with two forwards, after selling Randal Kolo Muani to Paris Saint-Germain for £77m this summer.
Mateta's stock is high in Germany after joining Palace from Mainz in 2022. Initially a £2.5m loan, Palace made the move permanent for £9m.
Palace blocked moves from RB Leipzig and Dortmund this summer after failing to sign a replacement. Mateta has not scored since netting a hat-trick against Plymouth in the Carabao Cup in August.