Free agency begins on Tuesday and the Dallas Cowboys have yet to re-sign running back DeMarco Murray, which further increases the chances the team loses him. If that's the case, who will be RB1 for the Cowboys in 2015?

It could be former Buffalo Bills running back C.J. Spiller. According to Mike Florio of ProFootballTalk, the Cowboys "will consider" Spiller in the event Murray leaves. It's a foregone conclusion Spiller won't be back with Buffalo after the team acquired LeSean McCoy from the Philadelphia Eagles in a trade last week. Spiller reportedly turned down a deal that would have paid him $4.5 million per season before that trade.

Murray is expected to receive a lucrative long-term deal after rushing for a league-high 1,845 yards on 392 carries and 13 touchdowns in 2014. It's unknown if Dallas will be able to keep him as they also have to work out a long-term contract with wide receiver Dez Bryant. It's unlikely both of these players give Dallas a discount.

"Murray did not get to cash in financially at the front of his career as a third round draft pick," writes Rick Gosselin of the Dallas Morning News. "He's 27 now, so this will be the only time in his life he'll be able to maximize his earning potential. I don't see him giving the Cowboys a hometown deal. I think he goes to the highest bidder ... I think there's less than a 25% chance he's back with the Cowboys in 2015."

The Cowboys have about $8 million left to spend and Jerry Jones said Murray is likely to hit the market, so they'll have to keep their options open. Spiller is certainly an attainable target, but his contract situation is a bit tricky. The 27-year-old has logged only 668 carries in five NFL seasons, but he's ranked second behind Bo Jackson for most yards per rush (5.12) in his first four seasons. He sits right in the middle of the pack in terms of potential earnings for free-agent backs.

Spiller's ability to perform as the primary back is unknown since he was splitting time with Fred Jackson and others during his time in Buffalo. Nonetheless, he's a dual threat, just like Murray, because he's a good receiving option out of the backfield. Murray's capability to carry the load was in question prior to the 2011 NFL Draft and he was selected in the third round by the Cowboys after being passed up for names such as Mark Ingram, Shane Vereen, Daniel Thomas, Mikel Leshoure and Ryan Williams.

Dallas has kept their offensive line together this offseason, which was perhaps the primary reason for Murray's success in 2014. If he leaves to join one of the other interested teams on the market, look for the Cowboys to add a player like Spiller to maintain that type of dynamic in the backfield.