Johann Van Graan says Munster have no choice but to move on from the Champions Cup defeat to Castres, but insisted they will seek clarification from the authorities regarding a number of incidents from the loss.

Munster sit top of Pool One after their narrow 13-12 loss to Castres, with the losing bonus point putting them three points clear of the French club.

In difficult weather conditions, the contest saw a number of flashpoints.

Marc-Antoine Rallier was sin-binned for his altercation with Peter O’Mahony, with the hooker perhaps fortunate to escape a red card.

Joey Carbery was hit with a huge tackle in the first half from Thomas Combezou, who then stood over the out-half and goaded the out-half, while Rory Kockott appeared to make contact with Chris Cloete’s face with his hand.

Speaking on BT Sport, Brian O’Driscoll called for the "sliding tackle" to be stamped out after Castres' Benjamín Urdapilleta slid in knee first on Andrew Conway as he attempted to ground the ball for a try.

An assistant referee told Castres number 8 to "stop" after hitting Sam Arnold in the head before half-time in a game that often threatened to boil over.

"What happens within the 80 [minutes], that gets dealt with. We have got to move on and we have a big game coming up this weekend," Van Graan told RTÉ Sport ahead of the upcoming game with Ulster.

Pressed further, he admitted that Munster will go down the usual route of speaking to authorities to get further clarification on some of the decisions made by referee Wayne Barnes.

"There is a process in place. We do the same each week, whether it is Pro 14 or Europe, you follow due process. You get answers to your questions. For us it is about clarity.

"It’s important that we keep up the values of the game"

"Obviously there were a few things that happened on the field of play…we just want some clarity on those.

"It’s important that we keep up the values of the game. There have been quite a few opinions on that, but we’ll move on."

Van Graan conceded that despite the chances created, his side "weren’t good enough" to take those opportunities and now is looking ahead to the next challenge.

Munster make the trip to Kingspan Stadium and while they eased to a 64-7 win over Dan McFarland’s weakened side in September, last year’s contest is more of a true reflection of the fine margins between the two sides.

On New Year’s Day Munster raced into a 17-0 lead, but with a player advantage courtesy of Sam Arnold’s dismissal, the home side fought back to win with 24 unopposed second-half points.

"Ulster have been playing brilliant rugby over the past few weeks," Van Graan said, highlighting their back-to-backs European wins over Scarlets.

"The quality of their play has been very impressive."

"It will be a very tough assignment for us."