Nine automatic spots will be determined in the final qualifying event at the Surrey venue, where Harrington will also announce his three captain’s picks soon after the final round on Sunday week.
McIlroy, Jon Rahm, Tommy Fleetwood, Tyrrell Hatton, Viktor Hovland, Paul Casey, Matthew Fitzpatrick, Lee Westwood and Shane Lowry are the players currently occupying those automatic berths.
But Austrian Bernd Wiesberger was on course to displace Lowry until he finished with a double-bogey 6 in the Omega European Masters in Switzerland last Sunday and more twists and turns possible both in this week’s Italian Open in Rome then that last qualifying lap at Wentworth.
“It depends how Italy and Wentworth go, I guess,” said McIlroy in reply to being asked if he felt Harrington was facing some tough phone calls before finalising the team to take on Steve Stricker’s US side at Whistling Straits later this month.
“Obviously, Bernd Wiesberger had a great chance to play himself into the team in Switzerland and didn't quite get it done but certainly has a couple more opportunities coming up in Italy and Wentworth to get over the line.
“I think if that were to happen, if say someone like a Bernd or a Victor Perez or one of those guys plays their way into the team, then I think it makes it a little more difficult for Padraig because then say, for example, if Shane doesn't get in automatically, then you're looking at him for a pick or whoever else.”
Ian Poulter and Sergio Garcia are the two leading contenders for picks, with MacIntyre, Justin Rose and Henrik Stenson among the others in contention to be on the plane heading to Wisconsin.
”It's still all a bit up in the air,” added McIlroy. “At this moment in time, if the qualification stopped, I think it's a pretty simple scenario, but a lot can change over the next couple of weeks.”
McIlroy, who confirmed he will not be playing at Wentworth, is “still pretty optimistic” that he can land the Tour Championship for a third time in Atlanta this weekend despite setting out eight shots behind in Thursday’s opening round in a staggered start.
“I think East Lake isn't the easiest golf course in the world; it seems to be a course that separates the field somewhat,” said McIlroy as he sized up his task in trying to catch leader Patrick Cantlay in the 30-man field.
“So the way I look at it, if I go out tomorrow and shoot six-under, for example, which is the score I shot last year in the first round, get to eight-under par, and some of those top guys shoot even par or even one or two over, all of a sudden you're right in it.
“I certainly don't feel like I'm out of it. I don't feel like I'm too far behind. Eight shots around this golf course doesn't seem like that much, so still pretty optimistic.”