Per Broncos executive vice president of public relations Patrick Smyth, Thomas was taken to a local hospital for further evaluation.
Mike Klis of 9News reported Thomas is being evaluated for a possible detached retina.
It's unclear how Thomas suffered the injury, though it occurred at some point in the first half.
He signed with the New York Jets last year before being released. Thomas joined the Buffalo Bills in October, and the team used him in 12 games last season. He played with the Indianapolis Colts early in the 2018 preseason, including their game against the Seattle Seahawks on Aug. 9, but was released two days later.
The Broncos signed Thomas on Aug. 13, giving him a chance to get playing time on special teams.