The luckless Sea Eagles co-captain slipped over trying to catch a Joey Walsh pass midway through Sunday's first half and cut a dejected figure leaving the field.
What initially appeared an innocuous fall could have major ramifications for the Sea Eagles, whose first season under Kieran Foran is losing steam at the worst possible time.
One win out of the top eight, ninth-placed Manly have lost four of their past five games and now face another stint without their talismanic, but frequently-injured, fullback.
The Sea Eagles posted a 5-2 record while Trbojevic nursed an injury to his other hamstring earlier in the year.
But the man who shone brightest during that period, back-up fullback Clayton Faulalo, is currently sidelined with his own hamstring issue.
The Sea Eagles must claim victory in four of their remaining six games to finish with a winning record but have difficult clashes against Cronulla, Newcastle and the Warriors to come.
Trbojevic's importance to Manly was reiterated as he and Jason Saab helped the visitors to a 10-0 lead inside six minutes on Sunday.
Saab tapped a Jamal Fogarty kick down for Trbojevic to score Manly's first, before the fullback threw the last pass for his right winger to score the first of his two tries.
Down eight points with 13 minutes to play, the Sea Eagles were given a golden chance to snatch the game back when the Titans lost winger Dean Ieremia to the sin bin for a hip-drop tackle.
But Manly were reduced to 12 men themselves after Josh Feledy committed a professional foul as the Sea Eagles were scrambling back following AJ Brimson's 70-metre tear.
In the next set, star fullback Keano Kini put Jojo Fifita in for a second try and made it a 12-point game in the last 10 minutes.
Tolu Koula's runaway four-pointer cut the deficit in the final minute, but it was too little and too late for Manly.
The 16th-placed Titans are no chance of playing finals but Josh Hannay's faith in his inexperienced players paid dividends in a fifth win of the year.
Rookie half Zane Harrison put Fifita into a hole ahead of the Queensland representative's first try and kicked through the line to help Brimson make it a 14-point game at the half.
Mature-age rookie Oliver Pascoe scored two tries in the game of his career and had a team-high 41 tackles at hooker.
Brimson returned a category one head injury assessment late in the game so is set to miss next week's clash with St George Illawarra.
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