Trbojevic was hurt in Manly's win over Wests Tigers last weekend but had been hopeful of facing the Titans on Saturday after scans cleared him of a serious injury.
The fullback had told Manly medical staff on Friday morning he expected to play, before he pulled up sore in a fitness test.
"He felt like he could have run and trained on Wednesday, so that was the most positive conversation I have had," coach Anthony Seibold said prior to the medical test.
"If he is feeling it at all, we won't risk him."
Manly have Kaeo Weekes on an extended bench, with the 21-year-old set to fill in at fullback in Trbojevic's absence.
The Sea Eagles are confident Trbojevic will be fit to face Brisbane next week.
Manly will take a longer-term approach with Josh Schuster.
The five-eighth has been held back this week after returning against the Tigers last Sunday.
The 21-year-old did not suffer any further damage in that match but Manly feel he needs reconditioning after calf and quad setbacks to start the year.
"Josh was medically cleared to play last week, and we played him. He didn't have his best performance in any way shape or form," Seibold said.
"We need Josh at his best.
"The performance staff, medical staff and Josh have a collaborative approach to give him the chance to recondition his injury and his body after a stop-start nine weeks.
"I have 100 per cent faith in him doing the job. I have shown I have his back with regards to what I think of him as a player.
"But he has to own his own career."
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