The Wales record appearance maker has been battling back from a chronic knee injury but has now been advised to draw the curtain on his illustrious career.
But he will play one more game for Cardiff Blues – his 195thfor the region – as they look to bounce back from last weekend’s defeat to Toyota Cheetahs
John Mulvihill has made five changes to the starting line-up with Lloyd Williams remaining captain.
In the backs, his younger brother Tom, who joined the region on trial at the beginning of the season, starts at full-back, and Rey Lee-Lo returns to the centre to partner Garyn Smith.
Up front, Brad Thyer and Kirby Myhill return to the front row, while Nick Williams starts at number eight.
Mulvihill said: “It should be a great day and a great occasion. Hopefully we can pack CAP and get a big crowd, because Gethin certainly deserves it.
“He’s played 195 times for this club, a 129 Test matches for Wales and he’s won everything in the game, bar a World Cup.
“He’s been there and done it and it’s really fitting that he plays in front of a home crowd on Sunday.”
Last week’s defeat in Bloemfontein brought an end to Wales’ Capital Region’s three game winning run in the competition, which was kick-started following a last gasp 26-24 defeat to Zebre in October.
The Blues are currently one-point off the play-off places and just eight points separate second and sixth in Conference A.
Mulvihill said: “It’s a massive game for us. If we beat Zebre this Sunday, we would have won five out of the last seven, and you’d probably take that. If it were to be four out of seven, that wouldn’t be acceptable for us.
“We need to make sure that we win this weekend. We want to make sure we send Gethin out as a winner.
“We want the crowds to come back because they enjoy the style of rugby we’re playing. If we win again this weekend, we’re setting ourselves up nicely for the rest of the season.”
Cardiff Blues: Tom Williams; Aled Summerhill, Garyn Smith, Rey Lee-Lo, Jason Harries; Steve Shingler, Lloyd Williams; Brad Thyer, Kirby Myhill, Scott Andrews, George Earle, Seb Davies, Josh Turnbull, Olly Robinson, Nick Williams.
Replacements: Kristian Dacey, Gethin Jenkins, Keiron Assiratti, James Down, Samu Manoa, Lewis Jones, Dan Fish, Harri Millard.