Weiskopf won the Open at Royal Troon in 1973, one of seven tournament victories in the year which also saw him make his first of two Ryder Cup appearances for the United States at Muirfield.
The 78-year-old, who won 16 PGA Tour titles, told Golfweek: "I've got a rough four to six months ahead of me.
"I had my first chemo today (Thursday) and the treatment lasted seven hours. I get the rest of the cocktail through my portable pump for 46 hours and then I get to rest up for 10-12 days before the next round."
Weiskopf caused a stir at the start of the month when he claimed Rory McIlroy lacks the determination to add to his haul of four major titles.
Weiskopf said that he feels "golf is something just for Rory to do", adding: "I don't think he'll win much more than the four he's got, or maybe five, because I don't see that determination and will to be the best."Meanwhile, the PGA Tour has announced today that the 16th Presidents Cup will be held at Medinah Country Club outside of Chicago in 2026.It will be the venue’s first team event since Europe pulled off a sensational last-day fightback to win the 2012 Ryder Cup.
The Presidents Cup is being held at Quail Hollow in Charlotte in 2022 before heading to Canada for the second time at Royal Montreal Golf Club in 2024.