Trevino believes that despite its short length by modern standards, the combination of the bunkers, small greens and forbidding rough will leave Tiger and co. with a very real test.
"That'll be the toughest little 7,000-yard golf course you'll ever see."
One of other challenges facing the players will be the unusually close proximity of the dining patio to the first tee.
Nerves jangling at the start of an important round, the players can almost hear the tinkle of cutlery and glasses as the members tuck in to some fine cuisine.
"It almost feels like you're teeing off in a carport because the first tee is just outside the door there," Trevino said.
"That's the way all the courses used to be. If you go over to Scotland and if you shank a ball out of a bunker, then you'll break the biggest window in the world in a dining room.
"That's the way they built it -- they had a lot of property, they didn't waste it. Now you're building golf courses on 500 acres and nine holes covers five miles!"
Merion, hosting the U.S. Open for the fifth time, takes up a mere 120 acres.
All about tradition
As Trevino and others have suggested, it is a course absolutely dripping with traditional influence and none more so than the clubhouse, which was once a farmhouse.
Players will use a changing room full of big metal lockers and period features.
Photos and old scorecards adorn the walls and there is a massive trophy case -- appropriate for a club which has hosted more USGA events, 18 in all, than any other in the United States.
The last was the 2009 Walker Cup amateur competition, where the likes of Rickie Fowler helped the United States to victory over Great Britain and Ireland.
Once on the course, players and caddies will have to do without yardage markers, while golf carts are prohibited even for members.
Graham has nothing but praise for the work of the club in preserving its culture and heritage.
"They've done such a superb job with their museum, they're very cognizant of the club's tradition and they do what Augusta National does. At all costs they protect the integrity of the club," the 67-year-old said.
"Certain (U.S.) Opens, like the one at Pebble Beach, is a little special and certainly the Open at Merion was special, especially for me."
Doubtless, whoever writes their name into the roll of honor under 2012 U.S. Open champion Webb Simpson will take away similar thoughts and join a list of special greats.