Flegler (shoulder) was unable to join the team captain's run on Thursday and joins centre Herbie Farnworth (shoulder) and second-rower Felise Kaufusi (hamstring) on the injured list for the top-of-the-table Dolphins.
Lock Max Plath and utility Kurt Donohue are suspended for Friday night's clash at Suncorp Stadium.
Flegler's replacement is 24-year-old middle forward Lachlan Hubner, who will make his NRL debut.
"Tom won't play. His arm is no good but Lachlan has had two years with us and played some trial matches as well," Bennett said.
"We have always been impressed with him and it is an opportunity for him. We are running short of middles and he is a middle.
"Just his work ethic (impresses me) and the type of bloke he is. He fits our culture."
In: ⬇️ Hubner - Out: ⬆️ Flegler — The Dolphins (@dolphinsnrl) pic.twitter.com/zWHAjqH5rVApril 11, 2024
The Dolphins also had everything go wrong before and during last year's 18-12 loss to Brisbane in round four.
They were without hooker Jeremy Marshall-King and Kaufusi due to suspension before a ball was kicked. Isaiya Katoa, then playing No.6, was unavailable due to injury.
Then they lost Kodi Nikorima to concussion in the 26th minute and halfback Sean O'Sullivan to a torn pectoral muscle in the 61st.
For the final quarter of the match they had no recognised playmaker on the field apart from starting five-eighth Anthony Milford.
All of that may have explained why coach Bennett looked forlorn in the dressing room after the 26-16 win over Wests Tigers last week when his star trio sustained their injuries.
Dolphins coach Wayne Bennett addressing the media after their win over the Tigers. (Jono Searle/AAP PHOTOS)
If it felt like Groundhog Day for the master coach after a suite of injuries to Kaufusi, Flegler and Farnworth, he wasn't showing it.
"I haven't thought much about last year. I'm only thinking about tomorrow," Bennett said.
"(The derby) is wonderful for the game and wonderful for the public. That makes it the great spectacle that it is with all the anticipation that goes with that.
"You look at the great sports of the world whether it is soccer, gridiron or basketball they have their local derbies and they mean a lot to everybody. This one fills the bill and everybody has bought into it."
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