Thornton (undisclosed) did not play in Thursday night's preseason opener against the Cardinals.
The wide receiver exited last Friday's practice with an injury. Ryan McFadden of ESPN.com reported that Thornton is expected to return to the field at some point during the preseason, but there is no specific week targeted. The Raiders' receiving room is currently wide open, and the more time the 23-year-old misses, the harder it will be to take one of the top slots.