The British Lions centre picked up a minor back injury in Tuesday night's 45-13 defeat at Pontypridd and will not be risked against the club he helped to the Allied Dunbar Premiership title last season.
Tait's absence allows former Scotland centre Graham Shiel a first full run-out of the season as the Reivers step up preparations for the forthcoming European Cup campaign next month.
Shiel will partner Scott Hastings in a new-look midfield pairing, with the versatile Cammy Murray starting on the left wing and Hugh Gilmour switching positions with Stuart Lang from right wing to full-back.
Up front, South African-born Scotland prop Matthew Proudfoot and lock Iain Fullarton are introduced to the pack, with the No 8 Brian Renwick taking over as captain in Tait's absence.
Glasgow Caledonians, meanwhile, have named a powerful line-up including 11 internationals for their third warm-up match against London Scottish at The Stoop on Saturday.
The Scotland captain Rob Wainwright and the hooker Gordon Bulloch are still missing, as is the winger James Craig, but the British Lion Tom Smith will continue his recuperation at loosehead prop.
The Scotland Under-21 lock Jason White has a further chance to impress as a blindside flanker in Wainwright's absence and, with Kevin McKenzie the only fit hooker, Glasgow Hawks' Chris Docherty has been drafted on to the bench.
The French international fly-half Thomas Castaignede is facing four months out with a shoulder injury. The Castre player will have a left shoulder operation next Thursday in Toulouse to resolve a problem dating back to May.
n England Colts won the second match of their Argentina tour with a 10- 8 triumph over Cuyo. The flanker Dan Collins scored England's try, with Ben Gollings converting and landing a penalty.Reuse content