Beale was ruled out of contention on Thursday for a spot in the team to take on NSW in the Rebels' Super Rugby opener in Melbourne but last year's John Eales medallist did not train with the squad all week and never looked a likely starter.
Gerrard, who filled in for Beale in their trial against the Crusaders a fortnight ago, will line up against another replacement fullback, Bernard Foley, for the Waratahs.
Cipriani said Gerrard, 29, performed ''very well'' against the Crusaders and would bring experience to the back line.
''A couple of weeks ago Mark filled [Beale's] place and he did very well,'' the English flyhalf said. ''Obviously Kurtley Beale is a world-class player and he's probably in the last two years been consistently the best back in the world, so it's obviously a big loss for any side, but we've trained this week appropriately and hopefully we'll go well at the weekend.''
The squad is hopeful Beale will be ready as early as next week, when the Rebels play the Reds in Brisbane.
The Rebels improved during each of their three trial matches, which started with a 36-0 loss to the Chiefs in a game in which four different sides were trialled.
They improved against the Blues, going down 31-21, and bettered that again against the Crusaders, losing 19-14.
Cipriani said the team was raring to play.
''We can't wait, this year we had three hard trials as opposed to last year [when] we had three easy trials,'' he said. ''I think they tested us, which is good, and then having the bye [in the first round] was just getting us ready, so this Friday we'll come out all systems and all guns blazing.''
Sydney-raised Luke Jones will start for the Rebels at blindside breakaway.
Teams:
Rebels:
15 Mark Gerrard, 14 Lachlan Mitchell, 13 Mitch Inman, 12 James O'Connor,
11 Cooper Vuna, 10 Danny Cipriani, 9 Nick Phipps, 8 Gareth Delve, 7 Tom
Chamberlain, 6 Luke Jones, 5 Hugh Pyle, 4 Adam Byrnes, 3 Laurie Weeks, 2
Adam Freier, 1 Nic Henderson.
Substitutes: 16
Luke Holmes, 17 Rodney Blake, 18 Alister Campbell, 19 Jarrod Saffy, 20
Richard Kingi, 21 Lloyd Johansson, 22 Julian Huxley.
Waratahs:
15. Adam Ashley-Cooper, 14. Tom Kingston, 13. Rob Horne, 12. Tom Carter, 11. Brackin Karauria-Henry, 10. Daniel Halangahu (captain), 9. Sarel Pretorius, 8. Wycliff Palu, 7. Chris Alcock, 6. Dave Dennis, 5. Kane Douglas, 4. Dean Mumm, 3. Sekope Kepu, 2. Tatafu Polota-Nau, 1. Benn Robinson
Substitutes: 16. Damian Fitzpatrick, 17. Paddy Ryan, 18. Lopeti Timani, 19. Jono Jenkins, 20. Brendan McKibbin, 21. Bernard Foley, 22. Nathan Trist