The duo have been retained by Wales coach Steve Hansen ahead of next weekend's RBS Six Nations opener against Italy. Hansen has enforced the rule allowing international coaches to call up players a week before a Test match. While both players feature in Hansen's plans ahead of the Rome clash, his decision has not gone down well at a club currently fighting for Zurich Premiership survival.
Bath assistant coach Brian Smith described the loss of Cooper and Thomas as a "blow" for the club.
Accordingly, Smith has had to bring Ross Blake into the squad as cover at scrumhalf, whilst Wales International Andy Lloyd is drafted into the forwards. There is also expected to be a return for England centre Mike Tindall who missed the defeat to Leicester with an injured hip.
Smith said that despite the changes, his side would be ready for the challenge that waits for them at Kingsholm.
"There will be a couple of changes to the line-up. Tindall is a big boost for us. But we will be without Gareth Cooper and Gavin Thomas, who will be with Wales. However, Andy Williams is an outstanding scrumhalf who can come in for Coops and is a player who deserves his chance.
"It will be an epic battle up front – like the last two weeks against the Saints and the Tigers. We have really held our own against Leicester. Now we have to make sure we convert our good possession and field position into points. We drew with them earlier in the season, and we are definitely a better side now.
"Gloucester are an outstanding side and deserve their spot at the top of the Zurich Premiership, but they are not invincible. Look at Munster – they did the near impossible when they defeated Gloucester in the Heineken Cup at Limerick. At the end of the day it is 15 on 15, or 22 on 22 – no side is invincible.”
The Bath squad:
Forwards: David Barnes, Andy Beattie, Steve Borthwick, Simon Emms, Alessio Galasso, Danny Grewcock (captain), Jonathan Humphreys, Andy Lloyd, John Mallett, Lee Mears, James Scaysbrook, Nathan Thomas, Adam Vander.
Backs: Olly Barkley, Ross Blake, Mike Catt, Alex Crockett, Simon Danielli, Kevin Maggs, Chris Malone, Matt Perry, Mike Tindall, Tom Voyce, Andy Williams.
Kick-off: 15.00 GMT