Mills' feared ACL rupture added a sour note to Sydney's remarkable 53-point qualifying final demolition of reigning premiers Brisbane at the SCG on Saturday.
Scans are expected to confirm the major knee injury for the luckless 29-year-old, who missed the Swans' 2024 grand final loss and has dealt with numerous untimely injuries across his 197-game career.
But Sydney have an opportunity to make amends for previous grand final losses, with a preliminary final at the SCG against either Fremantle or Geelong to come.
Papley admitted it "didn't look great" for Mills following the resilient skipper's first-quarter knee injury.
Mills has earned significant praise for leading the club amid the dramatic fallout from the events at the Pullman Hotel last month.
"He (Mills) is an amazing captain," Papley told the Nine Network on Sunday.
"(He's) been amazing over the last few weeks.
"He puts this club on his back and wears his heart on his sleeve. It's just shattering for him.
"I'd love nothing more than to win a premiership and have him by my side, albeit he might not be there (playing).
"He deserves it more than anyone."
Star players Isaac Heeney, Chad Warner and Nick Blakey - All-Australian contenders before they were banned from being selected - are among the five serving club-imposed bans.
Important tagger James Jordon and defender Riley Bice are the other Swans who won't play again this season.
Sydney were given little chance to knock off the Lions, even though they finished the home-and-away season second.
Even club chairman Andrew Pridham conceded the Swans' premiership hopes had been "torpedoed" after suspending the five players.
But all cylinders of the Swans machine fired on Saturday despite those major absences, with Errol Gulden calling the shots in the engine room as Harry Cunningham directed the defence.
Logan McDonald may have led with six goals, but Sydney enjoyed an even contribution from their forward line, with Charlie Curnow and Papley slotting five each.
Tall forward Hayden McLean's three-goal haul is set to further complicate coach Dean Cox's selection conundrum, with Joel Amartey (Achilles) nearing full fitness.
Star winger Justin McInerney is also expected to return from a hamstring strain for the preliminary final.
"They should both be available ... and that'll be a decision, like we do every week," Cox said of Amartey and McInerney.
Cox said Saturday's win felt like the most complete four-quarter performance in his tenure.
"With the quality of opposition that we were playing and the ability of the match-winners that they have all over the ground," Cox said.
"I was really proud when we've got some of the young kids that come into our football team to be able to execute the roles they had to play at the right time."
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