Melbourne NRL captain Cameron Smith says it's possible star fullback Billy Slater has cost himself the Dally M medal by opting not to play in the Storm's final round match.

According to the NRL playoff captains, Tuesday's Dally M medal night is down to a two-horse race between Slater and Wests Tigers ace Benji Marshall.

With Slater in the hunt to be announced as the NRL's best player for the first time, Storm coach Craig Bellamy apparently gave him the option to face the Sydney Roosters in Sunday's round-26 clash and try to add to his points tally.

However, Storm skipper Smith, who is a chance to win a second Dally M and was also sat out from taking on the Roosters, revealed Slater decided to put team before individual achievement and rest ahead of the finals series.

"It shows the culture that we have at our club that the team is before any player," said Smith.

"I think everyone knows he's in with a good chance of winning the Dally M but, if he went out (on Sunday) and played a good game, he may well have wrapped it up, but he put his team first and he needs to be congratulated for that."

Tigers captain Robbie Farah says five-eighth Marshall has been in career-best form and believes Slater and Smith's final-round week off will only boost his chances.

"He's definitely my pick and the fact Billy and Cam got rested last night will help him," Farah said.

"I think so (it's his best year). His last couple of years he's been injury free and that's coincided with him playing some great footy.

"Last year, he won the golden boot and, this year, he'll win the Dally M, so I think that speaks for itself."

Marshall is firming after his outstanding recent form lifted the Tigers to a top-four finish.

The New Zealand skipper described his year as inconsistent for the first part, and credited his teammates for giving him a chance at a maiden Dally M.

"I don't think I've done enough to deserve that award. There's a lot of other guys I think have really killed it and whatever happens, happens," Marshall said.

"(Form) was up and down, the year in itself was a tough year. My form was good for about six weeks and went missing for about eight and then started to come back.

"I'm really happy we're in the semis now and, off the back of a lot of my teammates taking a lot of the pressure off me, it's really made my job easier and helped me relax to play better."

When the voting went behind closed doors after round 16 of the competition, North Queensland maestro Johnathan Thurston was leading the voting on 24 points.

However, in the third State of Origin match, Thurston went down with a serious knee injury and pundits don't believe the superstar halfback has done enough to stay ahead of Slater and Marshall.

Cronulla skipper Paul Gallen was second in the voting after round 16, but his niggling injuries and the Sharks' ailing form have likely cost him a shot.

Slater (15 points after round 16), Cooper Cronk, Cameron Smith (both 14 points), Marshall (13 points) and smokey Chris Sandow (12 points) are all poised to challenge for the prize.

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