Merrin defended the club's decisions to let both Cartwright and Matt Moylan go over the summer break, indicating they were not on the same page with the rest of the squad.
Cartwright's exit at the Panthers was considered months in the making, and Merrin said modern day rugby league players were professional enough to adjust to sudden departures and arrivals regardless of when it occurs.
"Within the playing group there is a lot of clarity there," Merrin said ahead of the club's trial with the Sydney Roosters on Saturday night.
"We're a tight group of boys all heading in the right direction and when a few players don't feel like they're heading in that same direction then the club needs to make a decision.
"Obviously the club did what they thought was the best thing for the club. Those players that have left was best for their career.
"Both the decisions were made from the player [perspective] and best perspective from the club as well."
The 28-year-old threw his support behind head coach Anthony Griffin and the coaching staff leading into the new season, re-iterating there was no reason to suggest the side wasn't capable of improving on their semi-final finish in 2017.
"There's no issues within the group, the fans should be happy with that," Merrin said.
"It's one of the tightest groups I've been a part of. Every club has their own individual issues and get on top of them their own ways and that's what has happened at our club.
"You ask any one of these players here and they've got full belief and respect of the staff and officials we have at this club to make the right decisions moving forward.
"When those decisions were made obviously you have a friendship base at the club and they'll never be lost, but at the end of the day the club and player has to do what's best for themselves."
Merrin was confident any remaining off-field distractions will vanish if the Panthers can fix an irritating habit of making sluggish starts their Telstra Premiership campaigns, having done so for the past three seasons.
The side have won only two games in their opening five clashes in each season dating back to 2015 – including last year's tough two-wins, seven-loss record from their first nine fixtures.
"It's something we need to work on and talk about, to start fast coming into these trials and round one," Merrin said.
"We've put a lot of emphasis on starting our games fast and building the consistency on the back of that.
"The boys are anxious to get out on the field and pass the ball around, get some contact and play some footy. That's the main thing about trials – to get the timing right off the ball and defensive structures right and get used to the players left and right of you.
"We're all looking forward to it."
Griffin has not mucked around for the pre-season hit-out on Saturday, naming new recruit James Maloney alongside Nathan Cleary in the halves with Merrin, James Tamou and James Fisher-Harris to lead the forward pack.