Ulster will be without hooker Rob Herring for Friday night's BKT United Rugby Championship Interpro with Connacht at Kingspan Stadium.The Ireland international suffered an ankle injury in his side's 31-15 Champions Cup win against Racing 92 on Saturday, with the province this afternoon confirming he would miss the Round 8 derby.Luke Marshall, who injured his ankle in training last week, is also unavailable for selection for this Friday's game against Connacht, while Dan McFarland's side will be sweating on the fitness of out-half Billy Burns due to an arm injury.In better news, Sean Reffell will be available for the northern province having overcome a long-term ankle issue.The 25-year-old former Saracens back-row has been sidelined since January, but has resumed full training, and will be in line to make just his fourth appearance for Ulster over the festive period.Ethan McIlroy has also returned to team training this week after suffering a facial fracture in last month's win against Munster.Ulster come into Friday night's derby off the back of a morale-boosting win against Racing 92 on Saturday, which emphatically ended a run of three straight defeats.A win on Friday night would see Ulster climb to a minimum of fifth in the table - for the time being at least - while they will also be out for revenge after their 22-20 defeat to Pete Wilkins' side back in early November. Listen to live commentary of Ulster v Connacht this Friday 22 December on RTÉ Radio 1 Extra, and follow our live blog on www.rte.ie/sport and the RTÉ News app.