McIlroy ended a long wait for his fifth major by winning the Masters last year to complete the grand slam of golf's majors and backed up that victory by securing another green jacket in April.
Yet, his drought at his home major in front of an adoring crowd of fans goes on since his only British Open win at Royal Liverpool.
McIlroy has limited his appearances on the PGA Tour to prioritise the majors this year, playing just three non-major events since the Masters in April.
The Northern Irishman looked good in a seventh-place finish at last week's Scottish Open, which could have been even better but for a fog-disrupted third round.
"Obviously there was some good in there today, but there was some bad as well. So, I'm going to need to work a little bit over the next couple days to be ready for Thursday," said McIlroy.
"At least I know what I'm doing. It's a matter of trying to sort of rectify it."
Home favourite Fleetwood
Scheffler, by contrast, hit a new low in a frustrating season for the world number one at the Renaissance Club.
After a four-year run of 78 successive cuts made, the American failed to make the cut at the Scottish Open.
Any doubts over Scheffler's ability to master the seaside links conditions appeared to be put to bed in his dominant display to win at Royal Portrush 12 months ago.
"Getting some extra rest going into a major championship is never the worst thing, but I really hate missing cuts, too," said the American.
Matt Fitzpatrick finished in a tie for third at the Scottish Open to maintain his supreme consistency on tour that has seen the Englishman rise to third in the world rankings.
But Fitzpatrick has struggled to produce his best at the majors since winning the 2022 US Open.
He appears best placed to end the 34-year wait for an English winner of the Open, but Tommy Fleetwood is the local hero on his hometown course.
Fleetwood is still seeking his first major but got the monkey off his back after failing to win on the PGA Tour in a brilliant end to last season that saw him scoop the $10 million prize for winning the Tour Championship.
Aaron Rai is another of the English contenders after his shock win at the US PGA Championship.
Despite a boom period for European golf, the last three winners of the British Open have been American.
Behind Scheffler, world number three Cameron Young and US Open champion Wyndham Clark lead the American charge, while Jordan Spieth was the victor the last time the Open was held at Birkdale in 2017 and remains adamant his major-winning days are not over.
Only St Andrews has hosted more British Opens than the course on the Southport sand dunes since it first hosted the event in 1954.
The previous 10 editions of the tournament at Birkdale have produced some iconic winners such as Peter Thomson, Arnold Palmer, Lee Trevino and Tom Watson.
One of the shortest courses on the 2026 PGA Tour schedule, but boasting over 100 bunkers, precision is more important than power.
However, the players will not have to cope with the wild weather that can wreak havoc at the British Open with the UK in the middle of a heatwave and sunshine forecast for all four days of play.