Already ruled out due to injury were Dave Attwood, Luke Narraway and Greg Somerville and added to that list this week was full back Olly Morgan who picked up a knock whilst training with England this week.
Half backs Andy Williams and Tim Taylor also miss out due to injuries suffered at London Wasps last weekend.
As a result, England U20s international Freddie Burns will turn out at full back and former U20s international Dave Lewis returns at scrum half.
Paul Doran-Jones is preferred to Pierre Capdevielle at tight head and a reshuffled back row sees Peter Buxton on the blindside and Jake Boer packing down at number eight.
Of note amongst the replacements is the name of scrum half Jordi Pasqualin who is named on the bench for England U20s in Glasgow on Friday evening but receives a call up in the absence of Rory Lawson and Andy Williams.
The two sides have already met once already in the competition this season, at Kingsholm in the opening round of group matches when Cardiff snatched a 26-25 win with the last kick of the match.
Head Coach Redpath knows that the Blues will be a tough proposition on Sunday even though they have been affected by international call ups as well.
"Cardiff have been a pretty effective side over the past few years and I think that last season was probably their best season for a long, long time."
"Even with several internationals away, they've still got a very good squad. It's a very big challenge for us. It's a semi final, it's a one off game. It isn't four points at stake, it's win or lose."
"But, we've got a game to play no matter whoever takes the pitch for them. Our focus will be on the ones who are playing and not the ones who are missing. They'll still have a lot of good players in their side."
"We're aware of how dangerous they are, they've beaten us three or four times. We'll just look to learn from last week and push on to Sunday."
Freddie Burns; James Simpson-Daniel, Mike Tindall (capt), Eliota Fuimaono-Sapolu, Lesley Vainikolo; Nicky Robinson, Dave Lewis; Nick Wood, Olivier Azam, Paul Doran-Jones; Will James, Alex Brown; Peter Buxton, Akapusi Qera, Jake Boer
Darren Dawidiuk, Rupert Harden/ Alasdair Dickinson, Pierre Capdevielle, Adam Eustace, Andrew Hazell, Jordi Pasqualin, Tim Molenaar, Tom Voyce