Sydney FC's frustrating season has gone from bad to worse after captain Alex Brosque was ruled out for at least another six weeks due to a hamstring injury sustained against Melbourne Victory last week.

The former Socceroo will take no further part in the remainder of the regular campaign and is in doubt to play again this season even if the Sky Blues reach the finals. A diagnosis on Monday revealed his hamstring strain was not only worse than first thought but an entirely new injury to rather than an aggravation of a previous problem.

"It's a big blow. At the start of the year when we did our recruitment I was looking for Alex Brosque to be a key figure and one of our main goal scorers," Sydney coach Graham Arnold said.