The Sydney-born goalkeeper has every reason to want to beat the blues in his 150th match at national league level, with the game the first of three huge tests for Brisbane.
Reddy said it was important the team focused on getting three points against Sydney and started to edge closer to the top of the table.
"After these three weeks we're probably going to sit back and say whether we're going to be challenging for first, second or are we going to be a team that's fighting to get into the six," he said.
"In that respect it's going to be a big three weeks but this week is very important because we want to get three points and get three points closer to Sydney, who are on top."
After a loss to Perth last weekend, Reddy said he and the rest of the team were keen to give the home fans something to cheer about on Sunday.
"It wasn't the best game but it's now Friday and we're looking forward to Sunday's game," he said.
"We've got a big game this week and we can't be thinking about last week if we want to perform this week.
"I'm just looking forward to my 150th game this weekend and playing against Sydney, which is always a big occasion for Queenslanders."
The Roar have a good record against the Sky Blues of late, having gone unbeaten in the past seven encounters.
However, Brisbane boss Frank Farina said last weekend's result against Perth showed records counted for nothing over the 90 minutes.
"Even if you've beaten them 10 times before or whatever it doesn't matter," the Roar coach said ahead of his 150th game as a national league coach.
"It's who turns up on the day with their game and who plays better than the other team."