NINE-times major champion Gary Player believes Phil Mickelson faces a "monumental task" to achieve a clean sweep of major wins and said it would be "eating him alive" if he was perennial nearly man Lee Westwood.
Mickelson, who became only the second left-hander to win the British Open when he triumphed at Muirfield on Sunday, has set his sights on joining Player, Gene Sarazen, Ben Hogan, Jack Nicklaus and Tiger Woods by landing the full set of all four of golf's top prizes.
The 43-year-old American has five majors to his name, having also captured three US Masters crowns and one US PGA Championship, and needs a first win in the US Open to complete a career sweep.
"That is going to be the biggest challenge of all the majors for him," South African Player said. "Because he is not a good driver and when you play the US Open you will have to use your driver.
"This is a monumental task for him but he has got that thing called 'it', which the majority of people don't have. I think he will probably win it.
"You can't describe it," added the super-fit 77-year-old who attended last week's British Open and still looks as lean and trim as he did in his heyday. "It is a gift that is loaned to you from the man above."
Mickelson said a US Open triumph would cement his status as one of the greats.
"If I am able to make it a career grand slam, I think that's the sign of the complete great player," he said after emulating fellow left-hander Bob Charles's 1963 British Open victory at Lytham.
"I am one leg away and it's been a tough leg. There are five players who have done that and they are the greats of the game – you look at them in a different light."
Westwood looked the likeliest winner of the British Open when he went into the final round holding a two-stroke lead over the field.
The 40-year-old Briton, however, wasted a glorious opportunity to end his wait for a breakthrough major victory at the 62nd attempt as he slumped to a closing 75.
"He has to be bitterly disappointed," said Player. "He was in the perfect position to win the Open, over the last five. It was one of those days. It would be eating me alive but I am different."