The 24-year-old is set to miss the rest of the year after scans confirmed the injury sustained on Wednesday.
The Dalby-born forward was one of the Titans' best players last year, crossing over 11 times in 23 games to be their leading try scorer.
The latest setback is the second time he has suffered a serious knee injury after rupturing an ACL in 2019 when he was on the cusp of making his NRL debut for Newcastle.
Titans coach Justin Holbrook told AAP Fermor's latest setback was "really disappointing news for Beau and us", but backed him to get back to his best.
"He'll be fine. Unfortunately he has already been through this process before and knows what's in front of him," Holbrook said.
"He came back from that and was excellent, and he will be the same again. It's just going to take time.
"Everyone trains good in pre-season but he was leading our group in everything. We were all excited about how good a season he was going to have but unfortunately it will be next year."
Fermor's form last year merited selection in Queensland's State of Origin extended squad where he thrived in the Maroons camp under the tutelage of coach Billy Slater and his assistant Cameron Smith.
Fermor told AAP at the Titans season launch how keen he was to make his Maroons debut this year and to play outside new Titans five-eighth Kieran Foran and take his game to a new level.
His partnership with Foran was on show in the 40-16 trial win over the Dolphins where he was in devastating form on the left edge.
The Titans kick off their NRL season against Wests Tigers at Leichhardt Oval on Sunday and Holbrook said they would bring 24-year-old forward Sam McIntyre into the 17 and likely elevate Joe Stimson from the bench into the starting side to replace Fermor.
"Joe will probably go in and start. He has played plenty of back-row," Holbrook said.
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