Whoever comes out on top at the Liberty Stadium (kick-off 7.45pm) will qualify for European rugby’s top competition next season.
A huge crowd is expected in Swansea as both teams do battle with everything on the line.
The clash will be Pivac’s last in charge of the Scarlets before he succeeds Warren Gatland as Wales head coach following the conclusion of this year’s World Cup in Japan.
“We’ve given the players a few weeks off and after that we’ve built that up and put some contact in – I don’t think you can go a month without contact training,” Pivac said.
“We’ve built things up gradually and this week is a full week. We’ve spoken about the importance of the game and the players are well aware of that.
“We’ve got a proud history in the top echelon of European rugby and that’s clearly where the club would like to be next season.”
Pivac continued: “They’re great games with the Ospreys, aren’t they? Even in the round robin format they’re huge matches and we’ll look forward to playing away. With this extra game against the Ospreys there will be no lack of motivation for the challenge I’d imagine.”
Explaining his team’s injury news for the Ospreys clash, Pivac added: “Rob Evans has had the surgery we know about. Wyn Jones is battling away to try and get himself ready in time, he’s picked up a bit of a knee injury and that will be a call later in the week. Samson Lee has picked up a HIA in training.
“Aaron Shingler will miss the deadline – not through his knee but he’s picked up a back strain and hasn’t been able to train for the last 10 days or so. He won’t be risked.
“James Davies hasn’t scrubbed up in time so there are a few missing, but the good news is Jake Ball has trained really well so we’ll look to include him in the 23.
“Ryan Elias is back from a niggly shoulder so that’s another positive. In the backs Kieron Fonotia sustained a knee injury in training on Friday. Unfortunately he’ll be unavailable.
“Blade Thomson has come through and from a head injury point of view he’s been training and is available for selection.”
Ahead of facing the Ospreys the Scarlets have confirmed m that three more members of their current squad — Tom Prydie, Steff Hughes and Paul Asquith — have signed fresh deals with the region.
Prydie headed west from the Dragons in 2017, earning himself a Wales Test recall at the end of the campaign when he featured in the wins over South Africa and Argentina on the tour of the Americas.
The winger has played 32 matches over the two seasons he has been at Parc y Scarlets, scoring eight tries.
Hughes is one of the region’s many home-grown products. A former Wales Under-20s captain, he has also skippered the Scarlets when Ken Owens has been on international duty.
The 25-year-old centre made his regional debut in an Anglo-Welsh Cup match against Saracens six years ago and has clocked up more than a half century of appearances for the region.
Asquith was signed from Australian club side Western Sydney Rams in 2017 and made an instant impact in West Wales, crossing for a hat-trick of tries on his debut against a Scarlets Premiership Select XV in Llandovery.
He has been an integral member of the squad over the last couple of seasons with his versatility seeing him slot in comfortably at centre or wing.
The 25-year-old Australian Sevens international also played a key role in the Scarlets’ European journey last season with his match-winning score late on against Benetton providing the spark to a memorable campaign.
Scarlets general manager of rugby Jon Daniels said: “All three players have proven valuable assets for the Scarlets in recent seasons.
“Tom’s form in his first season saw him return to the international stage; Steff’s leadership and experience has seen him being given the responsibility of captaining the side, while Paul has been a great acquisition for us and has played a lot of rugby in the two seasons he has been here.
“We are delighted all three have signed new contracts and will be part of a strong and exciting squad for next season.”
The majority of the current squad at Parc y Scarlets will be on board for 2019-20.
Wales Six Nations Grand Slam winners Ken Owens, Jon Davies and Rob Evans have signed new deals, as has full-back Johnny McNicholl, prop Werner Kruger, as well as a host of home-grown talent.
The Scarlets have also signed second row Sam Lousi from Super Rugby side the Hurricanes.