URC referees' boss Tappe Henning has acknowledged to Munster that the match officials made errors in Saturday's narrow loss to the Bulls. But the Reds insist they have moved on with the focus on making the URC play-offs over their final three regular season games - and thus secure Champions Cup qualification for next season. Munster must finish in the top eight of the URC to play in European club rugby's top tier next season but have dropped to seventh after that damaging 16-13 defeat at Thomond Park, when they wrongly played with 14 men for 13 minutes in the second half. Alex Kendellen was told to leave the pitch from the 52nd to 63rd minute after tighthead Stephen Archer was forced off with a shoulder injury and uncontested scrums were in play for the remainder of the game. Archer had earlier come on for Oli Jager, but because Jager had failed a HIA then referee Andrea Piardi should not have reduced Munster to 14 men. Following Munster's intervention, the officials finally allowed Kendellen to return but it took 13 minutes. Ian Costello, the province's interim head coach and director of rugby operations, has since spoken with refs boss Henning. "I suppose the easiest way of putting it is that the officials made a mistake,” said Munster's assistant coach Mossie Lawler. “We chased the decision but we’re certainly not focusing on that. "Again, it’s not the reason we lost the game or we’re certainly not putting it down to that. Our view is that we’re looking forward to Cardiff and not looking back. I’m not going into the details of the conversation. They’ve admitted they’ve made a mistake and we left it at that.” Munster back row Gavin Coombes also spoke about the incident. “It’s a new week isn’t it, so park that and move on," he said. "There was great energy coming into the building this morning. Everyone knows this is a big week for us so it’s been put behind us. “It’s rugby, there’s a lot of rules, you know, and it is hard to keep track of. That’s just the way the sport is sometimes and unfortunately it didn’t work out for us at the weekend. “I think the frustration was mostly on our performance. We had opportunities to win the game, we had a lineout on their five and different attacking positions like that and we didn’t take them, so you always have to look at yourself first before you look outwards…we’re definitely focusing on ourselves.” Coombes is due back to action against Cardiff at the Arms Park on Friday after missing the Bulls loss with an ankle injury. Calvin Nash was also ruled out with an ankle injury, while Craig Casey was withdrawn before kick-off due to illness - like Casey, Peter O'Mahony took part in the warm-up but a tight hamstring meant he was not risked. Nash and Casey are expected to be available, while a call on O'Mahony will be made later in the week. John Hodnett has a toe injury and Diarmuid Barron has a shoulder and arm issue, and both are doubts, while Jager is out as he goes through return to play protocols. Lawler, meanwhile, pledged that Munster's full focus will be on winning the points in Cardiff and not what happened last weekend. “Of course it will," he said. "We’re in a situation now where we’re fighting for top eight. "Look, we’re seventh in the table, we’ve three games left and two of them are at home. So from our point of view, it’s what we can control. If we win our games, we stay in the top eight. So that solely has been our focus. The focus in relation to this week is only Cardiff. "We know the test ahead of us this week. Our reviews and previews this week has been solely on them.” Get the latest sports headlines straight to your inbox by signing up for free email alerts.