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The 25-year-old has been in fine touch with seven goals in his past six games but has succumbed to a hamstring niggle and tweeted this morning that he wouldn't be available for this weekend's game across the Tasman.
"Gym session done today!! Gutted to be missing the game on Sunday but confident the boys will come back with 3 points! #hatemissinggames," the All White tweeted.
Brockie's absence could hand Tyler Boyd a rare start against an Adelaide side that have performed above expectations under coach John Kosmina and sit in second place on the A-League ladder.
The 17-year-old Boyd has been a regular feature off the bench this summer with a slew of cameo performances but starting a game at Hindmarsh Stadium would be a big ask for a rookie.
Solomon Islands Benjamin Totori is another player who could start up front. Alternatively Phoenix coach Ricki Herbert could inject midfielder Louis Fenton into the line-up and reshuffle his personnel.
The Phoenix are sixth after 10 rounds of the competition.