Thorson was signed to the Giants' practice squad Saturday, Dan Salomone of the Giants' official site reports.
The quarterback will likely operate as a reserve option behind Jake Fromm and Brian Lewerke in Week 18 as both Daniel Jones (neck) and Mike Glennon (wrist) will be unavailable. Thorson has spent a large portion of the season with the Giants, allowing him to fill in if needed against Washington on Sunday.