The Lions’ 17-game unbeaten run in the Championship was ended by Slavisa Jokanovic’s side in late April. Fulham went on to win promotion to the Premier League via the play-offs.
Tunnicliffe, who made 50 league appearances for the Whites, missed Saturday’s 2-0 defeat at West Bromwich Albion with a broken toe.
“With Tunni it is a pain thing – we’ll have to look at his availability on Tuesday,” said Harris. “We have got some kicks and bruises from the weekend.
“There will be some personnel who played at the weekend that will be missing because of it. It will be an opportunity for some of our players out of the U23s and certainly some others who have been waiting to play.
“Tunni might be back on the training pitch at the start of this week. The game will have extra spice and he’ll want to be out there, with Fulham being his old club.
“There will be changes. We are searching for that successful formula. We are also in the middle of a relentless run of fixtures that has seen nearly every Championship manager moan about it over the course of the last four days. Next week we go Saturday–Wednesday–Saturday again, it really is astonishing we find ourselves in this position.
“We have got nine games in four weeks and that is a big ask – it’s a big ask for top sides who have a squad of 23 or 24 players. With us having a smaller squad it is even tougher.
“But we’ll try to use the cups as an positive. That has been the case in the past with the FA Cup and Checkatrade Trophy. We’ve had two wins [in the EFL Cup this season] and that has built momentum in small doses.
“This is an opportunity for us to play against a Premier League side in a derby and get back on the grass. We know it’s a tough game because Fulham have an outstanding squad and have added really well in the summer to the quality they already had. They have still dominated the ball in the Premier League.
“It will be a physical test for us without the ball and when we win it there will be fatigue in the legs from the work put in – we have to use the ball really wisely and really concentrate.
“I’m looking for a positive outcome – whether that is a result or performance over the 90 minutes. We’re trying to build in small steps.”