Horgan will line out on the right wing in a back-three that also features Rob Kearney (full-back) and Isa Nacewa (left wing).
In the pack, Leo Cullen skippers the side and is partnered at second row by Scotland's Nathan Hines.
Stan Wright continues in the front row alongside John Fogarty and CJ van der Linde, while the returning Kevin McLaughlin takes his place in the back row alongside fellow Irish internationals Shane Jennings and Jamie Heaslip.
Speaking ahead of Friday's crunch clash, Leinster coach Michael Cheika said: "Last week's win (over Munster) makes this week a bit easier and you've a bit more of a smile on your face for a preparation point of view, but that's about it.
"We've learned too many times in all competitions - whether it's in European back-to-backs, or Magners (League) to Heineken Cup, or Magners to Magners - that the last week means nothing unless you back it up the next week.
"This is sudden death football now, so I think it's going to come down to who wants it more on the night now.
"Clermont are a team who don't seem to have an issue about going away from home. They have shown their strategic prowess in the two matches they played in their pool against Leicester and the Ospreys.
"They're also very well managed and it's going to be the biggest battle of our season so far."
As well as the usual 'Family Day' activity, Bank of Ireland will also be staging a free pre-match Supporters 'Q & A' event, hosted by legend Reggie Corrigan, in the Supporters Bar behind the Anglesea Stand from 7.15pm with Leinster's Sean O'Brien and Rhys Ruddock.
There will be special 'Blue Magic' themed events inside the ground, while 'Simon Morgan and the Keynotes' will be performing live on the pitch before the game and at half-time.
As this match is a sell-out and there are expected to be traffic delays around Ballsbridge, supporters are encouraged to use public transport. There will be no tickets on sale on the night.
LEINSTER (v Clermont Auvergne): Rob Kearney; Shane Horgan, Brian O'Driscoll, Gordon D'Arcy, Isa Nacewa; Jonathan Sexton, Eoin Reddan; Stan Wright, John Fogarty, CJ van der Linde, Leo Cullen (capt), Nathan Hines, Kevin McLaughlin, Shane Jennings, Jamie Heaslip.
Replacements: Bernard Jackman, Mike Ross, Cian Healy, Malcolm O'Kelly, Stephen Keogh, Paul O'Donohoe, Shaun Berne, Girvan Dempsey.