Masters champion Rahm jumped from the PGA Tour to LIV on Thursday in a big-money move which sent another shockwave through the sport.
Rahm's former Ryder Cup team-mates Sergio Garcia, Ian Poulter and Lee Westwood were ineligible for Europe's win over the US in the biennial team competition this year after joining LIV Golf and resigning from the Europe-based DP World Tour.
The next Ryder Cup takes place in 2025 at Bethpage Black in Farmingdale, New York and McIlroy was in no doubt that Rahm would be there.
"Jon is going to be in Bethpage in 2025 so, because of this decision, the European Tour are going to have to rewrite the rules for Ryder Cup eligibility," four-time major winner McIlroy told Sky Sports in an interview published on Thursday.
"There's absolutely no question about that - I certainly want Jon Rahm on the next Ryder Cup team."
McIlroy also voiced his concerns over the future of golf with tours competing to sign elite players.
"You're basically cannibalising yourself as a sport, sort of the same as what boxing has done with all the different organisations and a few other sports have as well," he said.
"To me, having all the best golfers under the one umbrella is the best way forward because I think that's really what the public wants."
