The Cove, who stayed away from the club's elimination final win over the Western Sydney Wanderers, announced late on Tuesday that they would attend the home first-leg clash with City.
The Cove boycotted the Wanderers game due to the Australian Professional Leagues' decision to sell the Grand Final hosting rights to the NSW government for the next three years.
In a statement published on social media The Cove said they would postpone their boycott and attend Friday's match at Allianz Stadium. However, they said their presence was contingent on the APL acknowledging them in a public statement and meeting their request to establish a fan representative group.
"It's going to be massive," said Sydney defender Rhyan Grant. "I think that they're always our 12th man. I know it's very cliched to say but they make a big difference for us."
With their full support back on deck, Grant said Sydney were confident of upsetting City after their come-from-behind win over the Wanderers.
"That was probably one of the most satisfying victories in my whole career," said the 300-game right-back. "Coming off the back of that, I know that we're going to have to bring ourselves back down a little bit.
"That was a game of high emotion. We sort of have to re-evaluate and go again this week and make sure we don't get too carried away.
"I think it gives us a little bit of confidence going into this game."
City finished 11 points clear at the top at the end of the regular season but, as Grant was keen to underline, Sydney have beaten the Melburnian outfit already this year.
Sydney claimed a 2-1 win back in December and enter the two-legged tie having won four consecutive games for the first time in two years.
"They're a team of superstars, it's going to be up to us to see where we can see and get at them," Grant said. "It's definitely up to us, we're capable of beating them and it's a matter of showing up on the day."