Rossouw will start the match in Dublin alongside Juan Martin Fernandez Lobbe and Chris Masoe while France international flyhalf Frederic Michalak is on the bench.
Toulon have named an unchanged side from the one that started the 24-12 semi-final victory over Saracens.
Top 14 leaders Clermont have been boosted by captain Aurelien Rougerie's recovery from a thigh injury he picked up almost a month ago in a league game against Toulouse.
Flank Gerhard Vosloo is also fit after successfully nursing a thigh injury.
Teams:Toulon: 15 Delon Armitage, 14 Rudi Wulf, 13 Mathieu Bastareaud, 12 Matt Giteau, 11 Alexis Palisson, 10 Jonny Wilkinson (captain), 9 Sebastien Tillous-Borde, 8-Chris Masoe, 7 Juan Martin Fernandez Lobbe, 6 Danie Rossouw, 5 Nick Kennedy, 4 Bakkies Botha, 3 Carl Hayman, 2 Sebastien Bruno, 1 Andrew Sheridan
Substitutes: 16 Jean-Charles Orioli, 17 Gethin Jenkins, 18 Davit Kubriashvili, 19 Joe van Niekerk, 20 Steffon Armitage, 21 Maxime Mermoz, 22 Frederic Michalak, 23 Jocelino Suta
Clermont: 15 Lee Byrne, 14 Sitiveni Sivivatu, 13 Aurelien Rougerie (captain), 12 Wesley Fofana, 11 Napolioni Nalaga, 10 Brock James, 9 Morga Parra, 8 Damien Chouly, 7 Gerhard Vosloo, 6 Julien Bonnaire, 5 Nathan Hines, 4 Jamie Cudmore, 3 Davit Zirakashvili, 2 Benjamin Kayser, 1 Thomas Domingo
Substitutes: 16 Ti'i Paulo, 17 Vincen Debaty, 18 Clement Ric, 19 Julien Pierre, 20 Julien Bardy, 21 Ludovoc Radosavljevic, 22 David Skrela, 23 Regan King