Elkington was watching the U.S. Open before he made a backhanded compliment about McIlroy.
The World No.2 was making his first appearance since the Players Championship - where he picked up a rib injury - but clearly wasn't back to his best after posting a disappointing first round of 78.
McIlroy, along with Dustin Johnson and Jason Day, made history in becoming the first top 3 in the history of the World Golf ratings to all miss a cut at the same major.
That tweet included a screenshot of McIlroy's achievements on the course.
Elkington tried to respond by claiming Jack Nicklaus never discussed his earnings, but at that point, Elk was on the canvas and the judge had called for the bell, raising Rory's hand as victor. "It was 5 mill".
"That's why jack designed 100's of golf courses...and it's knew...mustn't have taught grammar in the 50's", McIlroy replied.
"But I'm not going to force it".
The plan now is for McIlroy to play three tournaments in four weeks to keep himself sharp going into the Open Championship next month.
"The worst thing I can do is go and force it because that's not my game".