Saracens are the first club to stage a European match in Brussels - with Farrell coming in as one of four changes.
Winger Chris Wyles, who will make his 100th appearance for Saracens, and scrum-half Neil de Kock also come into the pack.
Up front, there is just the one alteration following the 45-0 rout of Edinburgh - with Rhys Gill preferred at loosehead prop.
Mako Vunipola, Joel Tomkins, Richard Wigglesworth and David Strettle drop to the bench, where they are joined by Alistair Hargreaves and Carlos Nieto.
Racing have recalled Juan Martin Hernandez after the Argentina star missed last week's victory over Munster.
Hernandez starts at full-back, with Benjamin Fall moving to the wing alongside Juan Imhoff.
There is another change in the pack where Bernard le Roux is preferred over Masinivanua Matadigo.
Saracens: 15 Alex Goode, 14 Chris Ashton, 13 Owen Farrell, 12 Brad Barritt, 11 Chris Wyles, 10 Charlie Hodgson, 9 Neil de Kock, 8 Jackson Wray, 7 Will Fraser, 6 Kelly Brown, 5 Mouritz Botha, 4 Steve Borthwick, 3 Matt Stevens, 2 Schalk Brits, 1 Rhys Gill.
Replacements: 16 John Smit, 17 Mako Vunipola, 18 Carlos Nieto, 19 Alistair Hargreaves, 20 Andy Saull, 21 Richard Wigglesworth, 22 Joel Tomkins, 23 David Strettle.
Racing Metro: 15 Juan Martin Hernandez, 14 Benjamin Fall, 13 Mirco Bergamasco, 12 Fabrice Estebanez, 11 Juan Imhoff, 10 Olly Barkley, 9 Maxime Machenaud, 8 Bernard le Roux, 7 Jacques Cronje (capt), 6 Antoine Battut, 5 Francois Van Der Merwe, 4 Karim Ghezal, 3 Luc Ducalcon, 2 Dimitri Szarzewski, 1 Andrea Lo Cicero.
Replacements: 16 Benkjamin Noirot, 17 Eddy Ben Arous, 18 Juan Pablo Orlandi, 19 Fabrice Metz, 20 Julien Jané, 21 Masinivanua Matadigo, 22 Sebastien Descons, 23 Gaetan Germain.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The Barbarians are one of the top invitational rugby sides with a long history and classic rugby jersey.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Lions get ready for their matches with this green training jersey. It's what the players wear. Get in the Gear!
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
$29.99
The Lions are ready to get their Australia tour underway. They arrive in Perth on Monday.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.
