Gailey told Buffalo's WGR-Radio on Monday that Jackson was not feeling well on the flight home following a 37-31 loss at New England. Gailey wouldn't rule out Jackson from playing, but noted there's a chance he won't because the game's only days away.
A person familiar with the injury calls it "unlikely" that Jackson will play. The person spoke on the condition of anonymity because Gailey would only say that Jackson "might not be ready."
Jackson was hurt in the final minute after taking a blow to head while being tackled by linebacker Brandon Spikes.
UPDATE: Gailey confirmed Monday that after undergoing concussion evaluations, Jackson will sit out Thursday's game with a concussion.
The Associated Press contributed to this report.