Winnan, who has a cracked sternum – picked up whilst on Under-21 Six Nations duty, is replaced at fullback by Brett Sparg, leaving the veterans Horan and Castaignède at centre.
"We've brought Thomas into the centres to get his hands on the ball more often," explained coach Wayne Shelford. "He's a great footballer and we want him to be involved more and with Tim (Horan) playing inside him we expect him to inject some pace into the line."
On the right-wing Shelford has opted for the pace of Sevens specialist Richard Haughton, while at scrum-half Canadian Morgan Williams gets the nod with current England first-choice Kyran Bracken starting on the bench.
Up front, Robbie Russell switches with Matt Cairns at hooker, while Craig Yandell starts ahead of Stuart Hooper in the second row, alongside former French star Abdel Benazzi.
Hooper drops down to the replacements bench where he is joined by Tony Roques, Ben Johnston and new-boy Nathan McAvoy, who makes his first appearance in a match-day 22 since joining Saracens from rugby league club Bradford Bulls last month.
Shelford was well aware of the importance of Saturday's match, especially with Bath, who are battling for survival in the Premiership, in some sort of form at present.
"We are well aware of the importance of this game and that Bath are hitting some form with a lot to play for but so have we," he said.
"It goes without saying that we're looking for a win but we're also looking for enthusiasm, vibrancy, commitment and hunger, the guys have had some time away and we want them to come back on Saturday and perform."
Saracens: 15 Brett Sparg, 14 Richard Haughton, 13 Thomas Castaignède, 12 Tim Horan (captain), 11 Darragh O'Mahony, 10 Andy Goode, 9 Morgan Williams, 8 Kris Chesney, 7 Richard Hill, 6 Ryan Peacey, 5 Craig Yandell, 4 Abdel Benazzi, 3 Mike Storey, 2 Robbie Russell, 1 Christian Califano.Replacements: 16 Johnny Marsters, 17 Matt Cairns, 18 Stuart Hooper, 19 Tony Roques, 20 Kyran Bracken, 21 Ben Johnston, 22 Nathan McAvoy.
Kick-off: 14.15 GMT