Melbourne Victory will be without one of their key forwards for next weekend's blockbuster derby against Melbourne City, with James Troisi sidelined for the next month with a broken collarbone.

And Victory's attacking stocks will be further diluted if Marco Rojas, the Kiwi international, cannot take any part in the clash either.

Rojas scored for the All Whites in their 2-1 loss to Mexico in Nashville, Tennessee, but left the pitch with 12 minutes remaining with what appeared to be an injury.

The wideman is due back in Melbourne on Friday and it had been expected that coach Kevin Muscat would only use him for part of the game against City.