Friendship with pal Pedrie is on hold...
Diack says business comes first ahead of facing ex-Ulster comrade Wannenburg
They'll probably share a few words before the whistle blows but then it will be down to business for Robbie Diack, who starts for Ulster, and his friend, and fellow South African, Pedrie Wannenburg who will be waiting to enter the fray from Oyonnax's bench.
Theirs was a friendship forged during Wannenburg's time at Ulster with the former Springbok arriving in Belfast in 2010 - two years after Diack - before departing for Castres in 2012 and then moving to join Oyonnax at the start of last season.
Indeed, the pair, who both largely play back row but can also cover lock, have faced off before in this competition, when Ulster managed their first significant victory in France in the 9-8 arm-wrestle at Castres back in January 2013. Rest assured that Wannenburg - at 34, he is four years older than Diack and close to the end of his career - will be gunning to turn the tables this time around.
Diack smiles when Wannenburg's name is brought up along with the query as to whether they have been texting each other this week.
"I think it's between the wives with the texting," he says, "as they're trying to see who's involved in the teams.
"We were friends over here and our families and wives are very good friends," adds Diack who is in line to make his 156th appearance for Ulster in their first ever meeting with the French club who are in apparent turmoil after jettisoning their coach Olivier Azam on Thursday.
"We met up with them during the summer holidays over in France and, yes, we are very close friends but it stops on the field," he says of Wannenburg.
"We'll have a good catch-up but after the game as until then it's all business," he states with even his 30th birthday, last Thursday, taking a back seat over the job in hand.
Though Diack's appearance in Sunday's first away win of the season at the Dragons was only his second start this season, the two-time capped Ireland international's wealth of experience meant that having him on board for this European opener was always likely.
"I needed to get that 80 minutes behind me (at the Dragons) and was grateful for the opportunity I got and I thank Les (Kiss) for that," was his take on the Rodney Parade experience.
Indeed, the sight of him soaring to secure the ball at the tail of the lineout, to set up what was some impressive mauling from Ulster, was a wholly positive sign.
He adds: "Yes we worked on getting things right up front with our lineout and our maul as well as at the scrum.
"As a loose forward you want to be as versatile as possible and I suppose when you've got Nick Williams carrying the ball as well as he does, you want to get the ball to him so if I can work on my lineout abilities it will benefit the team," Diack says with the trip to France very much uppermost in his thoughts.
"For me, I wanted to work on my physicality and going into the Oyonnax game you really need that.
"They've a massive pack and will be very physical like most French teams and especially so at home.
"We know what it takes (to win in France) and we know where to take our bodies and our minds in games like this, which will be to dark places, but we're capable of doing that," Diack says regarding what lies ahead.
Indeed, any notions that this weekend's hosts will either be off-colour - Oyonnax are one from bottom of the Top 14 - or already just focusing on rescuing their badly faltering domestic season, instead of a first taste of Champions Cup action, are given short shrift.
"We're not looking at their record at the moment," he says while accepting that this pool opener still has the appearance of potentially delivering a key win on the road.
For Diack, though, it's also an opportunity to regain some lost ground.
"Hopefully I can prove myself this week," he adds. That catch-up with Pedrie can wait.