Rory Clegg starts for Glasgow against his former club. The stand-off made 55 appearances for Harlequins and helped them win the Premiership title in 2012.
Rory is now into his second season with the Warriors, after originally joining as cover during the Rugby World Cup last summer.
He moved to French side Oyonnax but re-joined Warriors in March.
Speaking to glasgowwarriors.org, Rory said: "It's been a few years now since I left Harlequins, but it's always good to go back.
"I have a couple of mates still there, so it'll be nice to see them and play against them tomorrow.
"They had a hit out last week against London Irish and they have a few of their big guns back this week, but it'll be a good occasion and the boys will enjoy it."
The Warriors squad have been training hard over the last couple of months and tomorrow's game is the first of three pre-season outings for Gregor Townsend's squad before the end of the month, with fixtures against Gloucester and Canada A lined up.
He added: "The boys are chomping at the bit to play now, we've been in pre-season for ages and it seems like forever since we played a game.
"Training has gone up a level this week and I think everyone is ready to play the game now.
"We train against each other every day and we all know the way we play, so it's good to get a hit out against a team with similar principles but won't know the calls like the boys do when we're training."
15 Fraser Lyle
14 Leonardo Sarto
13 Nick Grigg
12 Sam Johnson
11 Rory Hughes
10 Rory Clegg
9 Grayson Hart
1 Ryan Grant
2 James Malcolm
3 D'arcy Rae
4 Tim Swinson
5 Scott Cummings
6 Robert Harley
7 Simone Favaro
8 Lewis Wynne
Replacements: Pat MacArthur, Djustice Sears-Duru, Zander Fagerson, Tjiuee Uanivi, Callum Hunter-Hill, Ali Price, Hagen Schulte, Alex Dunbar, Richie Vernon and Junior Bulumakau