Cockle ruptured a tendon in his finger during the loss to Bath last week and is replaced in the staring line-up by Declan Danaher.
This is a further blow for the side – currently at 10th place in the Premiership standings – who already have key men Justin Bishop (ankle), Kevin Burke (knee), Glenn Delaney (ankle), Paul Gustard (torn biceps) and Richard Kirke (shoulder) out of action.
London Irish: 15 Michael Horak, 14 Paul Sackey, 13 Nick Burrows, 12 Brendan Venter, 11 Geoff Appleford, 10 Barry Everitt, 9 Darren Edwards, 8 Chris Sheasby, 7 Kieron Dawson, 6 Declan Danaher, 5 Bob Casey, 4 Ryan Strudwick (captain), 3 Rob Hardwick, 2 Naka Drotské, 1 Mike Worsley.Replacements: 16 Kevin Barrett, 17 Mark Mapletoft, 18 Nick Kennedy, 19 Adrian Flavin, 20 Kieran Roche, 21 Neal Hatley, 22 Simon Halford.
Kick-off: 15.00 BST (14.00 GMT)