SURPRISE, Ariz. -- In just about three weeks, the D-backs will need to finalize their 25-man Opening Day roster. While the bullpen is still very much a work in progress with three spots up for grabs, the battle on the position player front is a little easier to handicap since there is only one spot available.

"There is only one spot," D-backs manager Bob Melvin said. "But there's a lot of competition for that one spot."

Here is a brief rundown of the candidates and how things stand:

Ryan Roberts: Roberts seems to have impressed more than any of the candidates so far. Billed as being more of a hitter than a fielder coming into camp, Roberts has played well defensively and has showed versatility being able to play second and third. When more outfielders get sent to Minor League camp, look for Roberts to get a look at the corner outfield spots where he has played in previous years. He had minimal catching experience in the Minors, but certainly could fill in during an emergency behind the plate. His scrappy nature has endeared him to the coaching staff, as well as teammates.

Alex Romero: Romero reported to camp with a broken right hand, so he has yet to see any game action. Melvin said on Saturday that the outfielder is around five or six days away from getting into a game. The longer than usual Spring Training still gives Romero time to earn a spot, and the fact that he played winter ball likely means it should not take him too long to get his timing back. He is out of Minor League options and can play all three outfield positions.

James Skelton: Skelton entered camp as the favorite to nab this spot, because as a Rule 5 Draft selection, he would have to be offered back to the Tigers. Though slightly built for a catcher, Skelton has impressed behind the plate with his soft hands and strong arm. Against the Dodgers last week, he threw out a runner from his knees. He has played some second base this spring and done a decent job there. He will likely get a look at third and possibly in the outfield as the spring progresses. At the plate, he has not swung the bat well (2-for-17), but as the scouting reports said about him, he's shown a good feel for the strike zone, walking four times while fanning twice. The organization was very high on Skelton when it took him in the Rule 5 Draft, and he'll be given every opportunity to make the team.

Josh Whitesell: Whitesell has faced an uphill battle from the start, simply because he is limited to just first base defensively and his skill set mirrors that of Tony Clark, who is assured of a spot. It makes it hard to see how the D-backs could carry two players who are only first baseman, because that would leave Augie Ojeda as the team's only backup infielder for the other positions. Whitesell has swung the bat well during camp, and last year showed he doesn't have anything left to prove at Triple-A when he hit .328 with 36 doubles and 26 homers.

Josh Wilson: Wilson is an excellent defender. A natural shortstop, he can play all over the infield. He is known more as a defender than a hitter, but this spring has swung the bat well -- he was hitting .318 heading into Saturday's game. One factor working against him that is out of his control is that he is similar to Ojeda both in the positions he plays and in terms of production. Roberts might hold a slight edge over Wilson because he has a little more thunder in his bat coming off the bench.