"He's been super dehydrated, and I apologize, but I made the decision that he can not come back out onstage", Hill, also a country music superstar, told the C2C crowd.
"We've all been a little bit dehydrated traveling so much", she said, adding that it was her call.
According to Rolling Stone, McGraw fell to his knees, then sat down just after he finishing performing his hit "Humble & Kind".
"Tim McGraw was suffering from dehydration in Dublin this evening at the C2C show", the rep explained.
Country music star Tim McGraw has collapsed on stage during a show at the Country to Country festival in Ireland.
McGraw had performed Friday night in London as part of C2C, a three-day, three-city country-music festival.
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"But I made the decision that he can not come back out on stage".
A statement sent to The (Nashville) Tennessean on McGraw's behalf said the singer was tended to by medical staff onsite "and he will be fine".
His next scheduled concert is May 31st in Richmond, Virginia, as part of the Soul2Soul Tour with Hill.
On 3 March, he praised the United States sporting goods store Dick's, after it raised the minimum age for anyone buying guns or ammunition to 21 years.
McGraw has been in the news lately for his stance in favor of gun control. McGraw tweeted. "Walmart, Kroger, and L.L. Bean, too".
Hill and McGraw have been married since 1996 and have three daughters, Gracie, Maggie and Audrey.