The reigning champions were dealt a major blow when scans revealed Thompson will be sidelined for up to a month with a hairline fracture in his foot, ruling him out of the first two weeks of the finals series.

Thompson's injury setback follows the two match suspension handed down to Muscat, who failed in his appeal on Wednesday night.

And Brosque, on hand to promote Sunday's clash against Perth Glory at Parramatta Stadium, was quick to point out Melbourne's newfound vulnerability.

"I think it does," Brosque said when asked if the star duo's absence alters Melbourne's standing heading into the post-season. "I mean you take Muscat and Thompson out and they're two big losses.

"Muscat is generally the big rock at the back and gets them going forward and he's a good leader for them. Thompson just scores goals and is such a threat to any defence so to not have the both of them if that's the case it's a big loss for them.

"Every team's gone through that patch where a couple of players are missing throughout the season and the teams have done well regardless.

"So Melbourne, with (Carlos) Hernandez and (Tom) Pondeljak they've got enough big-name players there to still step up and do well, but I think having lost them two it's a big loss for them."

Melbourne currently hold top spot on goal difference ahead of Gold Coast United, with the Sky Blues two points adrift in third spot with two rounds remaining.

A revised six team finals series will see first and second play off over two legs for a berth in the grand-final, with the losing team granted a second chance in the Preliminary Final.

Brosque admits the Sky Blues have been guilty of getting ahead of themselves in the race for top spot in recent weeks, but is confident the side won't make the same mistake on Sunday.

"We tried to keep it (claiming top spot) in the back of our minds but not talk about it too much because you can get carried away, and we sort of did a little bit," he said.

"We started thinking about top spot too much ... and I think we probably got a bit carried away and stopped doing the things we were doing when we were winning.

"In the past couple of weeks we've come up with a few big games and we've won a couple and (also) haven't done so well like last week (against Brisbane Roar).

"So this week definitely, if we want to set up a big game against Melbourne in the last (round of the season) and if we want any chance to finish top two, needless to say this is a must-win and we need the points this week."