Dragons coach Paul McGregor has scoffed at suggestions Trent Merrin's demotion to the interchange bench for Monday night's season-opener has anything to do with the Origin star's decision to leave the club at the end of the season.

Merrin was on Tuesday named in the No 14 jumper for the clash with Melbourne, a day after informing teammates that he will join Penrith at season's end on a three-year $2 million deal. It meant his selection on the bench - where he started seven of his 21 games last year - raised some eyebrows but McGregor said it was purely about the team's overall game plan and not any form of retribution.

"It's got nothing do with anything but our interchange rotation," McGregor said.

"It's a 17-man game these days and the guys on bench will probably play a lot longer minutes than the guys who start. George [Rose] is obviously not going to play long minutes, so we'll put him out there to go as long as he possibly can, whether that's 10, 15 or 20 minutes, and then we'll put a player on there that can play long minutes.

"That's what Trent does, he brings good value to the group because he's a middle player that can play 60 minutes in a game and that frees up another interchange. We pick our best 17 available for the game we're playing and it was the right fit for Melbourne."

McGregor has named three other forwards on the bench alongside Merrin, with Rory O'Brien to debut and Jack de Belin and Mike Cooper also expected to be given long stints in the middle. It means hooker Mitch Rein will be called on to play the full 80 minutes after many expected him to share the role with veteran recruit Heath L'Estrange, who didn't make the 19-man cut.

"To start the year you need to rotate big men around quickly because it's the first game of the year and some will blow quicker than others," McGregor said.

"Mitch built into that 80 minutes against Warrington really well, so for the start of the year he's hardened and very fit. He's probably the fittest player in our team, so he'll handle the 80 minutes and that allows us to rotate our big guys around."

Merrin's announcement on Monday brought an end to several months of speculation regarding his future and McGregor said all parties were relieved the issue was resolved before round one.

"I think this stuff's gone on long enough, I'm sure he'd tell you that," he said.

"We made an attractive offer that wasn't quite attractive enough and he's decided to play somewhere else in 2016. At the end of the day it was a good offer but it wasn't good enough and Trent decided to move to Penrith and I respect his decision. The biggest thing for us now is that Trent's a valued part of our group and big part of our team in 2015. He can't wait, now it's all out of the way, to move forward and play this week."