Greenstock, who picked up a shoulder injury in the process, while Tiatia was cited for a dangerous tackle, has been replaced at inside centre by Nils Mordt in one of three changes to the Exiles' XV that lost 15-10 to Quins last Saturday.
The other changes made by London Irish head coach Gary Gold see Mark Mapletoft return at fly-half, having recovered from the knock he took in the game against Gloucester, while Phil Murphy replaces Paul Gustard in the back row.
"Last Saturday at the Stoop we played most of the rugby, yet were the authors of our own downfall by making too many errors and conceded penalties," said Gold.
"We are looking for a major improvement this week against a talented Leeds Tykes team."
London Irish: 15 Michael Horak, 14 Paul Sackey, 13 Geoff Appleford, 12 Nils Mordt, 11 Justin Bishop, 10 Mark Mapletoft, 9 Darren Edwards, 8 Chris Sheasby, 7 Kieron Dawson, 6 Phil Murphy, 5 Bob Casey, 4 Ryan Strudwick (captain), 3 Rob Hardwick, 2 Naka Drotské, 1 Neal Hatley.Replacements: 16 Pierre Durant, 17 Adrian Flavin, 18 Kieran Roche, 19 Declan Danaher, 20 Matt Cannon, 21 Kevin Barrett, 22 Barry Everitt.
Kick-off: 15.00 BST (13.00 GMT)