Club captain Flood starts at fly-half, with Allen returning at centre after missing last weekend’s bonus-point win over London Wasps at Welford Road.
There are changes in the front row where international props Marcos Ayerza and Logovi’i Mulipola return and Neil Briggs comes in to start at hooker.
Geoff Parling continues his return after shoulder surgery with a place in the 23 after playing 20 minutes as a replacement in the win over Wasps.
Director of rugby Richard Cockerill said: “The chase for the top four places is very tight and we’ve just got to keep picking up points. We haven’t got a semi-final spot yet so we’re as hungry as ever to get there.
“Quins are in good form, they played very well in their games against Stade Francais and Sale Sharks in the last two weeks, but we’ve been in good form too and we have to get our own game right going down there.”
Tigers will wear their alternate kit for Friday’s fixture which kicks off at 7.45pm and is scheduled for live coverage on BT Sport.
Leicester Tigers (v Harlequins, away, Friday 7.45pm)
15 Mathew Tait
14 Blaine Scully
13 Manusamoa Tuilagi
12 Anthony Allen
11 Vereniki Goneva
10 Toby Flood
9 Ben Youngs
1 Marcos Ayerza
2 Neil Briggs
3 Logovi’i Mulipola
4 Ed Slater (c)
5 Graham Kitchener
6 Jamie Gibson
7 Julian Salvi
8 Jordan Crane
Replacements
16 Rob Hawkins
17 Boris Stankovich
18 Fraser Balmain
19 Geoff Parling
20 Pablo Matera
21 David Mele
22 Owen Williams
23 Niall Morris
Harlequins
15 Mike Brown
14 Ollie Lindsay-Hague
13 Tim Molenaar
12 Jordan Turner-Hall
11 Sam Smith
10 Nick Evans
9 Danny Care
1 Joe Marler
2 Dave Ward
3 Kyle Sinckler
4 Charlie Matthews
5 George Robson
6 Luke Wallace
7 Chris Robshaw (C)
8 Nick Easter
replacements
16 Rob Buchanan
17 Mark Lambert
18 Paul Doran Jones
19 Tom Guest
20 Maurie Fa'asavalu
21 Karl Dickson
22 Ben Botica
23 Ross Chisholm
