The 27-year-old spent the pre-season with the Cleveland Browns, having left the Chicago Bears at the end of last season, but was released on September 1.
Offensive coordinator Darrell Bevell told the team's website: "It's somebody we definitely need for our depth at the position. We only had two and something could happen real fast, so we need to start training somebody to start to get them ready.
"He had a good workout. I like what we saw in the workout when we were deciding if we wanted to sign him. I liked the way he ran around, caught the ball real easy. I like what I saw. But it's still really, really early."
Davis recorded 229 receiving yards and two touchdowns for the Browns in 2012.