The biggest loss is clearly Hernandez though, who, while he hasn't shown his best for Wellington this season, directs traffic in the middle of the park for the Phoenix.
The Costa Rican's withdrawal means there will be a reshuffle of personnel in the midfield, which could see striker Stein Huysegems drop in behind a front two of Kenny Cunningham and the returning Jeremy Brockie, who has recovered from a hamstring complaint, while Paul Ifill may be given the chance to start.
Vince Lia and Jason Hicks seem destined to retain their places in the midfield for Friday's game.
"I feel that we have the squad to win this game because we've got good depth now,'' Merrick said.
Muscat, who played at left back during the 0-0 draw with Western Sydney last Sunday, will be replaced by Reece Caira who started the first six games of the season on the left-side of defence before he was rested last weekend.
Wellington are still searching for their first win of the season and have four draws and three losses to show for their efforts so far.
Perth, who occupy seventh on the A-League ladder while the Phoenix are in ninth, have experienced some injury problems in the past few weeks with the latest being striker Shane Smeltz, who could be sidelined for up to a month with an ankle issue.