Coates was on the comeback trail after injuring his Achilles in the pre-season, requiring surgery that put him out for three months.
With State of Origin off the table, the Storm set a target of round 10 for his return but that was pushed back with the Queensland representative flyer's recovery slower than expected.Â
Coates had resumed running and looking to integrate with the main squad in the next week when the 25-year-old suffered the crushing injury on Friday at training.
"I was running and it just popped," a shattered Coates told AAP.
"I was only running at about 50 per cent and it just went."
He is set to undergo another round of surgery after consulting a specialist.
With six wins for the season, Melbourne have missed the aerial threat of Coates and his try-scoring prowess, bagging 20 tries in 22 matches last season.
Coates attended the Storm's match at AAMI Park against Newcastle on Friday night and was wearing a moon-boot on his left leg and using a scooter to get around.
Melbourne coach Craig Bellamy said the players were told of their popular teammate's injury before the match and he believed team's effort in securing the 32-30 win stemmed from that news.
Skipper Harry Grant said it was "heavy" to hear and he hoped Coates would get back to his best.
"I think it was only a couple of weeks from returning ... Xav's the ultimate team man, he always puts everyone before himself, and you know what you're going to get from him week in, week out," Grant said.
"The club's got his back now, and I think for Xav, he knows that a lot of people have been through that injury and come out on top.
"What he's had has been pretty off and on, up and down, and he hasn't really been able to push through it, so I guess now he will get the repair done, the full rupture, and fingers crossed get on with a clean slate of the rehab journey."
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