Henry won an appeal this week of a proposed one-year suspension for a positive drug test in October. The decision came more than two weeks after his appeal was heard in Phoenix.
"If I thought the test was positive, Travis would not be on this football team," Shanahan told The Rocky Mountain News Nov. 12. "All the tests except the one test have come back negative. I couldn't tell you before because they've got to do retests. And they did those re-tests ... when I did find that out, that's one of the reasons that he's here."
The Broncos signed Henry to a five-year contract last off-season.
He has scored three touchdowns and picked up 629 yards on 143 carries in eight games this season.