The Rotorua first team will be without central midfielder Eru West after he suffered a hamstring injury against Otumoetai - a "big blow" for Walker to face.
"He's a big part of our team and has played excellently recently - he is a massive loss. It means a player will have to step up from our Championship side and put in a good game. I'm sure this will happen though," Walker said.
Walker said he was wary of an "unknown" Rangers opposition but was confident players would lift their performance in front of a home crowd.
"I haven't been able to do any research on them and don't know what to expect," he said.
"Every player wants a good run in the Chatham Cup and a good run here could give us lots of confidence in the league as well. It's a big one at home for us and that could make a real difference with support cheering us on. The cup raises performances because of the occasion."
Kick-off is at 2pm.