Arnold’s dismissal for a dangerous, high hit on Ulster fly-half Christian Lealiifano came with Munster already down to 14 men following a sin-binning for replacement lock Fineen Wycherley as the northern province staged a rousing fightback early in the second half.

It ultimately led to a second defeat inside a week after a St Stephen’s Day home loss to Leinster and van Graan must now expect a suspension for Arnold, who has been turning in impressive performances covering for the injured Jaco Taute and newly capped Ireland centre Farrell.

With Dan Goggin also rehabilitating a knee injury suffered on the first day of the season back in September, Munster’s midfield options have been stretched and required rotation on Monday saw inside centre Rory Scannell rested, with Arnold moving from 13 to 12 with Keith Earls moved off the wing to cover at outside centre.

The return of Farrell, 24, would be a significant relief ahead of a third derby in 11 days with Munster’s beaten matchday squad returning from Belfast to Limerick late on New Year’s Day while van Graan oversaw a training session at the High Performance Centre yesterday with 12 to 15 players who had been rested at home following the Leinster game.

The Munster boss will need all hands on deck given the exertions of Monday night which saw him lose the services of captain for the night Billy Holland to a failed Head Injury Assessment in the first half, wing Calvin Nash to a hip pointer problem at half-time and then forwards Niall Scannell (shoulder and rib), Tommy O’Donnell (shoulder) and James Cronin (calf) during the second-half meltdown.

All look likely to miss Saturday’s Thomond Park clash with Conference A rivals Connacht, who lost narrowly to Leinster at the RDS on New Year’s Day.

Scannell, like O’Donnell and Cronin, had only recently returned to action following injury and van Graan said the hooker had been “struggling to breathe” in the dressing room following his 52nd-minute injury.

“I think it’s his shoulder and rib,” Munster’s head coach said. “Niall looks pretty banged up, is in a lot of pain. Calvin Nash couldn’t take the field in the second half. We’ve only four days until we play again but luckily we’ve 12 to 15 guys back in Limerick training (yesterday) morning and most of them will play on Saturday. There will be multiple changes again. For this one a lot of guys got their opportunities. Pretty bruised down there. Lot of injuries, especially to key guys, you know, Niall, Billy, James, pretty important guys in our tight five.

“We’ve got to get on the bus, recover and then we’ve got two days of training and then we’re right back in it on Saturday.”

Arnold will find out today if he is to face further sanction as a disciplinary panel meets in Neath to decide his fate.

Van Graan said of Arnold: “He’s been a big part of our team over the last few weeks. Hopefully we’ll have Chris Farrell back this weekend. We’ll reassess him (after training).

“We’ll have Rory Scannell back and hopefully Dan Goggin within the next week or two, so at least we’ve got some depth in the centres.”

There will be little time to address Munster’s split personality performance with discipline an increasing concern given Wycherley’s sin-binning was a third yellow card in as many games, John Ryan at Leicester Tigers and Andrew Conway against Leinster being the previous transgressors. Indeed, Munster have had to play short-handed in five of the six games played since van Graan arrived at the province.

“I can’t really explain it, it’s just got to improve,” he said on Monday night before addressing the need to stop a losing run.

“It’s small margins, this game of rugby. We have got to change the spiral pretty quickly to get back to winning. If you’ve got an excuses mentality that becomes part of your game. There’s no excuses from our side, we did enough to win this game but didn’t take our opportunities in the first half and if you’re going to concede cards you’re not going to win games.”

This story first appeared in the Irish Examiner.