Rory McIlroy, Steve Elkington have heated back and forth

ERIN, Wis. -- Rory McIlroy fired back at fellow major champion Steve Elkington on Twitter on Friday night after the Australian golfer said the Northern Irishman "was bored playing golf'' due to having plenty of money in the bank.

McIlroy, who missed the cut at the U.S. Open after having played just one event in the past two months due to a recurring injury, responded to Elkington's tweet that said without Tiger Woods the "threshold'' for winning majors is probably four, with $100 million in the bank -- suggesting that McIlroy was satisfied.

McIlroy, who has four major titles, wrote: "More like $200-million. Not bad for a "bored'' 28-year old ... more where that came from.''

Elkington then replied that he knew McIlroy was a "money guy'' and that Jack Nicklaus won 18 major titles and never spoke about money. McIlroy, while correcting Elkington's spelling, pointed out that Nicklaus didn't earn much money as a player, hence his golf course design business.

An infrequent competitor on the Champions Tour, Elkington won 10 times on the PGA Tour, including the 1995 PGA Championship in a playoff over Colin Montgomerie.

He also won two Players Championships, but his career was often sidetracked due to injuries and severe allergies.

In recent years, Elkington has had his share of controversial moments on Twitter, such as insensitive remarks made after a fatal helicopter crash in Scotland and racially insensitive comments made about people from Pakistan while playing at the Senior British Open. He also ridiculed former Missouri football player Michael Sam when he announced he is gay prior to the 2014 NFL draft.