The Scarlets know that a win will be enough to secure Champions Cup rugby next season but Treviso are in the same situation.
Sixth-placed Scarlets have a four-point buffer to Connacht, with Edinburgh a point further back in the race for the final Champions Cup spot.
Treviso meanwhile lead their local rivals Zebre by three points, with the Italian Champions Cup spot on the line.
The Italians have lost six on the spin in the league but they pushed Leinster hard last week before eventually going down in Dublin.
The Scarlets won their derby encounter with the Blues and are now on the verge of Europe's top competition in what will be Rhys Priestland's final game for the club.
The fly-half is off to Bath at the end of the season, and gets the start at fly-half for Wayne Pivac's side.
Gareth Davies, Rob Evans and Adam Warren come into the side, as Pivac makes three changes from the team that beat the Blues.
Meanwhile Corniel van Zyl will make his final appearance for Treviso before returning to his native South Africa at the end of the season.
Form: Treviso require a victory to guarantee their place in next season's European Champions Cup, but have been defeated in their last six Guinness PRO12 encounters since beating Cardiff Blues at Stadio Monigo at the end of February. As it stands Scarlets require two points from this fixture to guarantee their participation in Europe's top tier tournament next year. The Welshmen have won their last three Guinness PRO12 matches since tripping up at home to Edinburgh in round 18. Scarlets are unbeaten against Italian sides for the past two seasons. Scarlets have won their last three encounters with Treviso since the Italians were victorious at Parc y Scarlets in round 22 of the 2012/13 campaign.
Treviso: 15 Jayden Hayward, 14 Andrea Pratichetti, 13 Luca Morisi, 12 Enrico Bacchin, 11 Simone Ragusi, 10 Sam Christie, 9 Henry Seniloli, 8 Mat Luamanu, 7 Francesco Minto, 6 Paul Derbyshire, 5 Corniel van Zyl, 4 Antonio Pavanello (c), 3 Rupert Harden, 2 Davide Giazzon, 1 Matteo Zanusso
Replacements: 16 Albert Anae, 17 Romulo Acosta, 18 Salesi Manu, 19 Marco Fuser, 20 Meyer Swanepoel, 21 Nicola Cattina, 22 Angelo Esposito, 23 James Ambrosini
Scarlets: 15 Liam Williams, 14 Adam Warren, 13 Hadleigh Parkes, 12 Scott Williams, 11 Steff Evans, 10 Rhys Priestland, 9 Gareth Davies, 8 John Barclay, 7 James Davies, 6 Aaron Shingler, 5 Lewis Rawlins, 4 Jake Ball, 3 Peter Edwards, 2 Ken Owens, 1 Rob Evans
Replacements: 16 Ryan Elias, 17 Phil John, 18 Wyn Jones, 19 George Earle, 20 Rory Pitman, 21 Rhodri Williams, 22 Steven Shingler, 23 Daniel Jones
Date: Saturday, May 16
Kick-off: 16:00 local (15:00 BST)
Venue: Stadio Monigo
Referee: George Clancy (IRFU, 72nd competition game)
Assistant Referees: Giuseppe Vivarini, Simone Boaretto (both FIR)
Citing Commissioner: Alberto Recaldini (FIR)
TMO: Carlo Damasco (FIR)