“We’ve got to be careful with that because then these national opens lose the fabric of what they are,” said McIlroy, the two-time Masters champion.
“You can’t call yourself a national open any more if it’s a closed-off tournament and there’s a certain number of guys.
“These events need to be treated differently than the Travelers Championship or RBC Heritage or whatever else is going to be in the Championship series.”
The Scottish Open has been co-sanctioned by the PGA and DP World Tours since 2022.
That means it can be played by members of either tour if they are ranked high enough to be eligible for the 156-man field.
PGA Tour CEO Brian Rolapp’s approved plan is for the Championship tier to feature fields of about 120 players competing for prize funds of at least $20m (£15m).
The Scottish Open purse is £6.7m, but MacIntyre said: “I personally think the Scottish Open is going to be totally fine.
“I don’t see it being a $20m event. I see it being a Rolex Series/European Tour event. It would be a bit mad to put a $20m event in Scotland given the world we live in today. It’s not the same as America.”
Many leading Americans are pleased to play in the Scottish Open in order to hone their games on a seaside links before The Open the following week.
“It needs to work within the new schedule,” said world number one and reigning Open champion Scottie Scheffler.
“It’s an important one that we keep it in the Championship Series just because you get so many guys that come over here and play the week before [The Open].”
Scheffler said it is “hard to tell” whether the field should also include DP World Tour players under the new set-up.
“Golf is so difficult to rank players when they are not playing together all the time,” said the 30-year-old American.
“Having similar guys playing against each other on great golf courses week in and week out is the best way to set up our schedule.
“To have this tournament fit into that mould would be really nice.”
Scheffler is in the afternoon wave of starters for the first round of the Scottish Open on Thursday, teeing off at 13:43 (BST) alongside Matt Fitzpatrick and Tommy Fleetwood.
McIlroy is off at 08:28 with MacIntyre and Chris Gotterup for company at the Tom Doak-designed East Lothian links.