A shoulder injury kept him out of last Sunday's first leg, when Glasgow went down 37-8 at Vicarage Road, Watford. Harrison replaces Matt Proudfoot, and in the only other change in the starting line-up Rory Kerr will be at full back instead of Moffat">Stuart Moffat. Kerr played at Watford as second-half replacement for Moffat.
Commenting on Kerr's recall, Hugh Campbell, Glasgow's head coach, remarked: "We're just changing it a wee bit. We're looking to do something different."
Glasgow: Rory Kerr, Gareth Maclure, Graeme Morrison, Andrew Henderson, Sean Lamont, Dan Parks, Graeme Beveridge, Euan Murray, Gordon Bulloch, Lee Harrison, Andrew Hall, Nathan Ross, Cameron Mather (captain), Donnie Macfadyen, Jon Petrie
Replacements: Scott Lawson, Andrew Kelly, Rory McKay, Roland Reid, Sam Pinder, Calvin Howarth, Moffat">Stuart Moffat
Saracens: Richard Haughton, Denis Cech, Paul Bailey, Ben Johnston, Darragh O’Mahony; Thomas Castaignede, Morgan Williams; Steven Sparks, Robbie Russell, Ben Broster, Simon Raiwalui (captain), Alex Codling, Ben Skirving, Ben Russell, Kris Chesney
Replacements: Johnny Marsters, James Parkes, Craig Yandell, Ryan Peacey, Kyran Bracken, Nicky Little, Daniel Legge
Two of the replacements for the match against Saracens, Sam Pinder and Calvin Howarth, are among eight Glasgow players available to play Premier One rugby on Saturday, and they could find themselves in opposition in the GHA v Boroughmuir match at Braidholm, though that will depend on how much game time they have against Saracens. Pinder and Alan Bulloch are available for GHA and Howarth for Boroughmuir.
Glasgow have also released Jon Steel and Kenny Sinclair for Ayr, David Millard and Andrew Wilson for Aberdeen Grammar School FP and Simon Gunn for Kirkcaldy.