In the front row, Jon Dawson comes in at tighthead in place of Laurent Gomez, who fractured a bone in his leg in training on New Year's Eve and will be out of action for approximately four months.
The other change sees Ace Tiatia selected on the blindside flank to replace Pat Sanderson, who came off with an injured shoulder against Bath. This selection means a shift across the back row to openside for skipper Andre Vos.
"This weekend’s game is a big one for both teams," said NEC Harlequins Chief Executive Mark Evans. "After our disappointing performance against Bath it is important that we bounce back immediately."
"Bristol are a very good unit and have some very exciting players. They are a very good team going forward and we know that we will face a tough challenge on Saturday afternoon."
NEC Harlequins: 15 Nathan Williams, 14 Rob Jewell, 13 Will Greenwood, 12 Chris Bell, 11 Dan Luger, 10 Paul Burke, 9 Nick Duncombe, 8 Tony Diprose, 7 Andre Vos (captain), 6 Ace Tiatia, 5 Alex Codling, 4 Bill Davison, 3 Jon Dawson, 2 Tani Fuga, 1 Jason Leonard. Replacements: 16 Pablo Cardinali, 17 Jim Evans, 18 Simon Miall, 19 Luke Sherriff, 20 Scott Bemand, 21 Ben Gollings, 22 Viliame Satala Kick-off: Saturday, 1500 GMT