The Northern Irishman, 25, said on Tuesday that he was without his clubs, 24 hours after his arrival in Dublin.
"Landed in Dublin yesterday morning from Newark and still no golf clubs," McIlroy tweeted.
United Airlines replied: "Your clubs will be in tomorrow and we'll deliver them to the tournament for you."
McIlroy was returning from the US Open at Pinehurst in North Carolina, where he finished 15 shots behind runaway winner Martin Kaymer.
The Irish Open at Fota Island starts on Thursday, with McIlroy attempting to win the tournament for the first time.
Rory McIlroy's preparations for this week's Irish Open in Cork were disrupted when his clubs went missing during a flight from the United States.