When former European Ryder Cup stalwarts left the established tours for LIV Golf riches in 2022, Rory McIlroy spoke of feeling 'betrayal'.
Rahm was confirmed as the breakaway tour's biggest signing to date on 7 December after weeks of intense speculation.
Rahm cited time commitments but his weeks of conspicuous silence allowed every golf fan on the planet to read between the lines.
It is unknown how much money Rahm is being paid up front but multiple publications suggests his fee is £450m.
McIlroy spoke to Sky Sports' Jamie Weir about Rahm's decision to leave the PGA Tour.
The four-times major champion previously declared rival league players shouldn't be allowed to compete at the biennial dust-up.
"But I think this week of all weeks, it's going to hit home with them that, you know, they are not here," McIlroy told reporters in Rome in September before leading Luke Donald's Europe to a four-point victory.
The four-times major champion now wants the rules to be changed to allow Rahm to be on the team at Bethpage Black in two years' time.
He told Sky Sports' Jamie Weir: "As someone who has played on three Ryder Cup teams with Jon... 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, absolutely, there is no question about that.
"I certainly want Jon Rahm on the next Ryder Cup team."
Asked about Rahm's decision, McIlroy continued: "I am going to miss competing against him week-in-week-out.
"He is such a good player, he has so much talent. He is so tenacious, and a great teammate at the Ryder Cup. I have nothing but good things to say about Jon. I respect the hell out of him as a golfer."
McIlroy, 34, continued: "He seems like he wants to live his life the right way. He wants to be a good dad, a good husband. You can't judge someone for making a decision that is the best thing for them.
"I would like to think the Ryder Cup means as much to them as it does to me. Maybe it does. But knowing what the consequences could be, I just could never make that decision.
"Okay, it might not be 100 per cent certain but that it could be the outcome? It just isn't a move I would be willing to make. I thought they felt the same way."
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