On a night when Haumole Olakau'atu reasserted his NSW credentials with two tries, the Sea Eagles were left reeling by Brooks' suspected anterior cruciate ligament injury.
The in-form five-eighth landed awkwardly in a tackle from Trent Toelau during Saturday's first half and did not return after the break.
"It's a suspected ACL (rupture). It's absolutely devastating for Luke," said Manly coach Kieran Foran.
"We're all shattered for him. Obviously we'll wait for confirmation on it but they're pretty certain it is, which is just gut-wrenching."
Brooks' replacement Walsh then went to the sin bin for injuring Ativalu Lisati in a hip-drop tackle and is likely to be charged by the match review committee.
Storm coach Craig Bellamy indicated Lisati will require syndesmosis surgery and face a stint on the sidelines.
Large and newly re-signed Walsh are considered Manly's brightest halves prospects since Foran and Daly Cherry-Evans, though Large has not yet made his NRL debut.
But if Walsh is suspended, coach Foran would have little option other than to blood the highly-rated 18-year-old for next week's clash with Parramatta.
Back-up playmaker Brandon Wakeham is currently sidelined with a calf issue, while journeyman hooker Zach Dockar-Clay could moonlight in the halves in a pinch.
"I'm not going to speculate just yet," Foran said on Large's hopes of a debut.
"We've got a number of players knocking on the door that could potentially fill that hole if Joey's not there.
"It's too early to tell, we'll just get over this one and then see what damage has been done by tomorrow."
Controversially axed for the second State of Origin game, Olakau'atu terrorised Melbourne's understrength left edge by scoring twice from crash plays inside 11 minutes.
He finished with 150 run metres, only hours after NSW selection rival Liam Martin had a tough night in Penrith's shock loss to North Queensland.
Already without Xavier Coates, Nick Meaney and Jack Howarth, the Storm's injury crisis deepened when fellow outside backs Joe Chan (back) and Moses Leo (concussion) went down mid-game.
"We're struggling there a bit," Bellamy said.
"I didn't think it was quite as bad as the scoreboard looked, but having said that, I would have liked for us to have played in the first half like we played in the second half.Â
"That was the disappointing thing for me."
The Sea Eagles feasted on the depleted edges, racing out to a 24-0 half-time lead and never looking likely to be chased down.
Pushing for his own Origin recall, Manly fullback Tom Trbojevic was his busy self, throwing the last pass for Tolu Koula to make it a four-score game in the first half.
Trbojevic made a try-saving tackle on Storm winger Siulagi Tuimalatu-Brown just after half-time and finished his second game back from injury with 141 metres.
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