The Reds (5-3), who sit fifth, face the third-placed Blues (6-3) on Saturday as part of Super Round at Christchurch's new One NZ Stadium.
Harry McLaughlin-Phillips will wear the No.10 for the Reds while Ben Volavola has been added to the bench with both Lynagh (calf) and Carter Gordon (knee) sidelined.
McDermott (hamstring) hasn't played all season while Lynagh has made just one second-half cameo off the bench, the club attributing his absence to a combination of leg injuries and illness.
The pair were mainstays in the Reds backline last year and regulars for the Wallabies last season.
"It's tough ... it does suck because you want them on the field," McReight said.Â
"But it's about next man up and we have the depth and the boys are really delivering, far beyond expectation."
In previous seasons the Reds have shown title-winning potential but faded at crucial times to surrender at the quarter-final stage.
There is hope there is another gear to reach this year with McDermott, Lynagh and Gordon - as well as fit-again prop Massimo De Lutiis - bursting to make late-season impact.
"There's a lot of rugby left and they're itching to get back, but we rip in this weekend," McReight said.
Coach Les Kiss said McLaughlin-Phillips had grown his game to adapt to the Reds' strategic development and erase thoughts of rushing Lynagh back.
"We're looking after him in every aspect," Kiss said of Lynagh, who was heavily targeted in his three starts against the British and Irish Lions last year.
"Finding ways we can make sure we keep progressing to get him right.
"He's still a young guy and we're not overly cautious, just measured."
The Reds and Blues have built a strong rivalry in recent seasons and will again meet on Anzac Day.
An added twist this year is that Blues coach Vern Cotter will replace Kiss at Ballymore once the Reds coach takes over the Wallabies later this year.
"Massive occasion," Kiss said of the clash.
"(Super Round is) something that Christchurch can be very proud of and for ourselves, it's a tight table and the bottom line is we have to do our business and then the pressure comes on other teams."
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