In the front row, Chris Horsman replaces Lee Fortey - who faces eight weeks on the sidelines as he awaits surgery for a dislocated shoulder - while twin brother Chris Fortey comes in for Ben Gotting at hooker.
There's a welcome return to the bench for prop Tony Windo for the first time this season following back surgery, while winger Marcel Garvey comes in to the 22 alongside Shane Drahm and Ryan Powell.
"The plan on Sunday is no different from the plan for the past couple of weeks," says director of rugby John Brain of the Vicarage Road match. "We're putting systems into place to improve our position. On the field, that revolves around improving our defensive record.
"Phil Larder has started this week and we continue to work hard on our set piece, and that will be boosted when we get our international players back. Our back-line attack needs improving too. We're working hard on all those areas. I would expect to see improvement in at least one of those areas on Sunday."
At the end of a "traumatic" week, he has paid tribute to departing head coach Anthony Eddy as a "fine man" who worked "extremely hard and introduced a lot of systems into this club that will benefit it for many seasons".
And he welcomed the return of veteran Windo.
"No one should underestimate how much he's been missed," he said. "If you ask any of the players, they'll say he's probably the most important member of the squad, with the exception of no one.
"He carries the utmost respect, he has a massive input and I'm sure that Pat (Sanderson) relies on him very heavily as captain of this club."
Team: 01 Darren Morris, 02 Chris Fortey, 03 Chris Horsman, 04 Tim Collier, 05 Craig Gillies, 06 Kai Horstmann (c), 07 Tom Harding, 08 Drew Hickey, 09 Matt Powell, 10 James Brown, 11 Mark Tucker, 12 Thomas Lombard, 13 Dale Rasmussen, 14 Aisea Havili, 15 Thinus Delport
Replacements: 16 Tony Windo, 17 Ben Gotting, 18 Phil Murphy, 19 Gavin Quinnell, 20 Ryan Powell, 21 Shane Drahm, 22 Marcel Garvey