Tiger Woods' former caddie, Steve Williams, revealed that the former world number one sometimes lacked respect for him.
The New Zealander was the bagman for Woods from 1999-2011, during which the 14-time major winner was ranked world number one for most of the time.
However, Williams revealed in his autobiography – which was released on the weekend – that the winning partnership was far from rosy.
"I was adamant that some of his behaviour on the course had to change," wrote the 52-year-old.
"He was well known for his bad temper and, while that was not pleasant to witness, you could live with it because it ended as quickly as it started.
"But he had other bad habits that upset me. I wanted him to prove to me he could change his behaviour and show me‚ and the game of golf, more respect. One thing that really [got to me] was how he would flippantly toss a club in the general direction of the bag, expecting me to go over and pick it up.
"I felt uneasy about bending down to pick up his discarded club, it was like I was his slave. The other thing that disgusted me was his habit of spitting at the hole if he missed a putt."
The US President was among the viewers watching the TaylorMade Driving Relief.
The US President phoned in as McIlroy played in a Sunday fundraiser for coronavirus victims.
Syme donated his prize money to charity.
‘This is the life of a caddie…’
The Northern Irishman is ranked number one in the world.
Players entering the United States will face a 14-day quarantine period, while a strict testing regime will be in place at each tournament.
The experienced duo will be involved at Whistling Straits.
The world number 98 intends to split the 10,000 euros prize money between his own charity and a hospital in his native Rotterdam.
The biennial event between Europe and the United States is scheduled to take place from September 25-27.