Walters and Leadbitter are both suspended after picking up their fifth yellow cards of the season in the 3-1 win over Blackpool on December 12 and will serve one-match bans after last weekend's game at Scunthorpe was called off.
Striker John is on loan from Palace and is ineligible play against the Eagles as part of the loan agreement between the two clubs.
Defender Alex Bruce (groin) and winger Lee Martin (ankle) could return as Keane's side look to extend their unbeaten run to 11 games.
David Norris is close to being involved for the first time since injuring his knee in the opening weekend of the season, while winger Luciano Civelli could be back in the new year from a knee injury of his own.
Goalkeeper Richard Wright remains sidelined with a serious knee injury.