Boyd was in ominous touch for Metro, booting three goals in the first 10 minutes of the game before marking another inside-50 entry midway through the opening term.
But this time instead of lining up for his fourth goal, Boyd landed awkwardly on his left ankle and was helped from the ground.
The key forward, projected to be this year's No.1 draft pick, didn't return to the field and will have scans on his ankle this week after ending the game on crutches with his leg in a moonboot.
Early diagnosis suggested it is unlikely Boyd will play in Metro's final two division one games against South Australia and Vic Country.
"He was pretty good in that first quarter," said Vic Metro coach Martin Allison.
"The ball was coming in really quick, he was getting perfect supply from the midfielders and he was finishing the work off.
"He's got to have scans and we'll know [more then]."
Metro overcame the loss of its main target to record the 15.10 (100) to 12.9 (81) win in the first clash of the NAB AFL Under-18 Championships between division one sides.
After breaking to a 30-point lead at the first change, which Metro held onto by half-time, Western Australia came back in the second half and even closed to within six points in the final term.
But Metro had too many contributors. Ben Lennon kicked four goals and added some class close to goal, while small forward/midfielder Mitch Honeychurch put in a best-on-ground showing.
Injury issues with his wrists restricted Honeychurch's influence early in the season but he was prolific against WA, gathering 33 disposals, (17 contested), seven clearances and two goals.
"I was rapt for him, I thought he was fantastic," Allison said.
"He's had a really interrupted summer and pre-season but players like Mitch really impressed today."
Josh Kelly had 29 disposals and chased hard through the middle, while Ben Cavarra (26 disposals) and Luke McDonald (25) played disciplined games.
Forwards Jonathon Marsh and Cameron McCarthy impressed most for Western Australia.
Marsh is tall and strong but has some extreme speed, which saw him turn a Metro opponent inside out in the last term to boot one of his three goals. Another was a booming 55-metre set shot.
McCarthy had only 10 disposals but had a presence with clean hands and three goals, while Blaine Johnson kicked four goals.
Alec Waterman, son of former West Coast Eagle Chris, had 23 disposals and five tackles.
Follow AFL website reporter Callum Twomey on Twitter at @AFL_CalTwomey.