Joe Schmidt has returned to New Zealand after a family bereavement but will be back in Dublin for Ireland's clash with Italy on Saturday.
Assistant coach Andy Farrell has taken control of Ireland's training for the early part of the week.
Former England coach Farrell will replace Schmidt as Ireland boss after the World Cup.
Ireland will start their tournament warm-up programme by facing Conor O'Shea's Italy at the Aviva Stadium on Saturday.
"Unfortunately, Joe had to go back to New Zealand due to a family bereavement," said scrum coach Greg Feek.
"On behalf of the team, I'd like to pass on our condolences to Joe and his wider family."
Ireland have spent the first half of the summer in gruelling pre-season preparations ahead of the World Cup, with their opening match in Japan against Scotland slated for September 22.
Schmidt's men will face England at Twickenham and home and away fixtures against Wales after Saturday's Italy encounter, to complete their warm-up schedule.
Ireland released lock Ultan Dillane and centre Rory Scannell earlier this week, with both now unlikely to be called back into World Cup plans barring injuries.
Munster lock Jean Kleyn comes into contention for his debut against Italy having survived that cull.
"We had quite a big squad and you just have to start making some calls," said Feek.
"We had six locks and a few outside backs there too.
"They did really well. But these are the tough calls we have to start making.
"There's definitely some areas we're still discussing."
