Who's out at running back for Dolphins?

Knowshon Moreno is in at running back for the Miami Dolphins. Moreno signed a one-year, $3 million contract with Miami and projects to be the immediate starter coming off a career season with the Denver Broncos.

But who is out at tailback for the Dolphins? That is the next question to consider as Miami and first-year general manager Dennis Hickey moves forward with his roster.

The Dolphins now have a full group of tailbacks that includes Moreno, Lamar Miller, Daniel Thomas, Mike Gillislee and Marcus Thigpen. Not all five tailbacks are going to make the 53-man roster.

The most the Dolphins would keep is four running backs. Moreno and Miller, last year's starter, are locks. Thigpen has versatility as Miami's primary kick returner and also experimented a little at wide receiver. Position flexibility is important to Miami third-year head coach Joe Philbin, and that could help Thigpen stick.

Most likely, Miami would have to choose between Thomas and Gillislee. Thomas is a former draft bust who never lived up to his potential. He was a second-round pick by former Dolphins general manager Jeff Ireland in 2011. But Thomas' career high is 581 rushing yards during his rookie year. Gillislee didn't get to show much his rookie year in 2013.

It will be a healthy competition at running back, both for starting roles and to make the roster. Moreno, who rushed for 1,038 yards last season, is clearly an upgrade in the starting lineup. But adding Moreno pushes someone out on the back end.