Spieth's caddie unable to finish 3rd round due to heat exhaustion

Just 11 holes into the third round at the Dean & DeLuca Invitational, Michael Greller knew he couldn't go any further.

Greller, who caddies for Jordan Spieth, was forced to hand over the golf bag to Spieth's physical trainer, Damon Goddard, because of heat exhaustion.

"He didn't tell me at all until we were walking down the 11th and he said, 'Hey, this is my last hole.' I was kind of surprised," Spieth told the Golf Channel after a round of 68. "I thought he was acting a little strange, a little quite, but I guess it just got him early on today."

Saturday was unbelievably warm in Fort Worth, Texas, with temperatures reaching a heat index of 108 degrees.

"He was running off to restrooms every time he saw one. I think it was just to get in the shade or pour water over himself or whatever it was," said Spieth.

Greller was treated on the property by the medical staff, and is expected to return to work for Sunday's final round.