South Sydney star recruit Adam MacDougall's season ended after he snapped his Achilles tendon in his side's 50-4 belting by Melbourne at Olympic Park.

MacDougall, 29, fell awkwardly in a tackle with less than two minutes to go in the National Rugby League clash.

The disconsolate former State of Origin and Test back, who had been outstanding for the Rabbitohs so far this season, was helped from the field by a trainer.

His and Souths' worst fears were confirmed immediately after the match.

"Adam's out for the season - he's pretty upset," Souths coach Paul Langmack said.

"It just went in the last tackle, moved forward and fell over right at the end."

It capped off a dreadful night for the Rabbitohs, who were given a defensive lesson in a nine tries to one shellacking by the Storm.

Late Storm inclusion Jake Webster, who replaced injured centre Ben MacDougall in the starting side, grabbed a hat-trick while Storm forward Danny Williams celebrated his 200th NRL game with two tries.

The Storm scored four tries in the first half to race to a 22-0 halftime lead, then killed off the game as a contest inside the first minute of the second half when Williams scored his first try to open the floodgates.

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