Palmer began the season as the starter but has played in just one game due to a nerve issue in this throwing shoulder. Palmer visited a nerve specialist in Denver over the weekend and is reportedly optimistic he could play against Washington.
Stanton started each of Arizona's last three games but sustained a concussion against the Broncos. Thomas entered the game in the third quarter to replace Stanton and completed one of his eight passes, an 81-yard touchdown to running back Andre Ellington.
Thomas was a fourth-round pick out of Virginia Tech in this year's draft.
The Cardinals signed former Pittsburgh Steelers quarterback Dennis Dixon to their practice squad Tuesday. Cardinals head coach Bruce Arians was the Steelers' offensive coordinator during Dixon's tenure in Pittsburgh.
Arizona is 3-1 this season and tied for first place in the NFC West.
- Dan Gartland