But with Simon Easterby's side facing their biggest game of the season at Ravenhill, the Wales pivot steps in to replace Owen Williams at No. 10.
Priestland is joined in Easterby's team by a number of current Welsh internationals with the Scarlets' head coach naming what looks a hugely experienced side.
They will though, have to improve following a disappointing performance against Treviso at Parc y Scarlets. The Italian side outscored the Scarlets by four tries to one in a convincing win though Easterby is adamant his side cannot play that badly again.
"All that happened last week against Treviso has been firmly put to bed now," he said.
"We are one of four teams that have 80 minutes of rugby in front of them to prove their ability and battle for a place in the final.
"This is where we wanted to be this season. We've achieved a top four finish, now we have to bring everything we have to this game to back up all the hard work we've put in throughout the season."
The introduction of Priestland is one of three changes made by Easterby from the Treviso defeat. Hooker Emyr Phillips replaces Matthew Rees on the bench while Gareth Owen also features as a replacement in place of Gareth Maule. Rob McCusker, who was withdrawn late against Treviso with a rib injury, returns to captain the side.
There are also starts for George North, who was forced off against Treviso, and fellow Welsh internationals Liam Williams, Jonathan Davies, Scott Williams and Aaron Shingler.
Ulster will go into the game as favourites though prop John Afoa is unlikely to be involved due to a hamstring problem.
But Easterby says his side are more than capable of surprising the Irish province.
"We've used last Friday as a motivator to produce the sort of performance you'd expect from a top four side and from the Scarlets jersey," he said.
"Ulster have been pretty much unbeatable this season and they are in the driving seat at home.
"But sides will be threatened by the players we put on the park, there's a good mix in our team and we know the quality that key Scarlets players can bring to our performance.
"It's going to be a huge night for us - we have this opportunity in front of us now and we'll give it everything we have."