Eustace, who has played at number eight in the A League this season, replaces the suspended Gareth Delve with Luke Narraway ruled out for several weeks following back surgery.
Other changes see James Simpson-Daniel return on the wing having recovered from the illness that ruled him out last weekend and Rory Lawson resume his half back partnership with Nicky Robinson.
In the pack, Olivier Azam makes his first start of the season at hooker whilst Peter Buxton forms a new look second row duo with Alex Brown and Alasdair Strokosch returns on the flank.
Having lost their two previous Guinness Premiership outings, Gloucester will be looking to bounce back this weekend but face a tough task as they take on unbeaten Saracens.
Head Coach Bryan Redpath admitted that there had been some tough talking done after the home defeat to Northampton last Saturday.
"Last weekend was disappointing in that our enthusiasm and energy levels weren't where they should be. Northampton came with a simple gameplan. They didn't have to beat us, we beat ourselves."
"But this weekend is based on a reaction to what happened last weekend. We've done our analysis and we highlighted individuals and highlighted the team work ethic in front of everyone to make sure no-one can hide."
Redpath acknowledged that Saracens are on a high at the moment:
"They are obviously buoyant after the first three games. They've been away from home and won well."
"They have a fairly simple game plan. They kick and chase well, they challenge at the breakdown. They're very efficient in what they do."
"It's a tough ask but after last weekend we need to get our side of the situation sorted."
Gloucester Rugby:
Tom Voyce; James Simpson-Daniel, Mike Tindall (capt), Eliota Fuimaono-Sapolu, Lesley Vainikolo; Nicky Robinson, Rory Lawson; Alasdair Dickinson, Olivier Azam, Paul Doran-Jones; Peter Buxton, Alex Brown; Alasdair Strokosch, Akapusi Qera, Adam Eustace
Replacements:
Scott Lawson, Shaun Knight, Pierre Capdevielle, Apo Satala, Andrew Hazell, Dave Lewis, Freddie Burns, Charlie Sharples
