Mooney, 28, said on Saturday it would be hard for the close-knit side to experience again a situation akin to last year's when ruckman Mark Blake was pushed aside in favour of former club captain Steven King.
"There is going to be a hard luck story because Chappy will obviously come in, so it will be disappointing for someone," he said.
"We went through it last year with Blakey and we're going to go through it again this year with someone, I'm not sure who.
"It's going to be very difficult for someone."
Mooney said the playing group wouldn't discuss the issue as a whole and would
instead wait for the coaching staff to make the decision.
He said it would then be up to the players to support their omitted teammate.
"I don't think we'll address it as a team. The coaches will work it out by Wednesday and the unlucky person will be told by then, I'd say," he said.
"As soon as we find out, obviously our heart will go out to the person.
"To be honest, it's very hard to even come up with a word. All you can do is support them and give them a pat on the back and a hug, because they're going to go through a really tough week."
Travis Varcoe, David Wojcinski and James Kelly had been touted as possibilities to be shifted out for Chapman, but coach Mark Thompson was quick to throw his support behind all three after Friday night's preliminary final win.
"Travis won't go out," Thompson said after the 12.11 (83) to 7.12 (54) victory.
"Travis wouldn't be considered [for omission].
"I'll say that publicly; if he doesn't get a virus he'll play next week.
"That was the best game he's played. I don't mean to be a smarty, but I was very happy with his game.
"Wojcinski did enough, kicked a goal and won enough of the ball to say he'd probably stay in. And [it was] good to have Kelly back. [I'm] glad that he's got the run and Wojcinski's got the run they needed before the Grand Final."
Thompson revealed on Channel 7 on Friday night that Blake's last-minute exclusion from the 2007 premiership side almost caused the ruckman to walk away from the game.
Mooney said on Saturday the Cats were extremely grateful he didn't.
"It was pretty disappointing for him and he took it pretty badly, as most people would," he said.
"But he's turned himself around and he's been a tremendous player this year. so thank God he didn't go in the end because he's been so good for us."
