This year's PGA Championship will take place without defending champion Phil Mickelson.
On Friday, Mickelson officially withdrew from the event at Southern Hills Country Club. He has not competed with the PGA Tour since January after making controversial remarks about Saudi Arabia's human-rights violations in reference to their LIV Golf Invitational Series.
When discussing Mickelson's absence ahead of Thursday's opening round, via Golf Digest, McIlroy called the situation "unfortunate" and "sad."
"This should be a celebration, right?" McIlroy said. "He won a major championship at 50 years old. It was possibly his last big, big moment in the game of golf. I think he should be here this week and celebrating what a monumental achievement he achieved last year."
In February, Mickelson acknowledged Saudi Arabia's "horrible record on human rights" but said he nevertheless viewed their new league as "a once-in-a-lifetime opportunity to reshape how the PGA Tour operates."
McIlroy called Mickelson's remarks "naive, selfish, egotistical, ignorant" and "disappointing." However, he later softened his stance.
"Look, Phil will be back," McIlroy said in March, per Sports Illustrated's Bob Harig. "I think the players want to see him back. He’s done a wonderful job for the game of golf, and he’s represented the game of golf very, very well for the entirety of his career. We all make mistakes. We all say things we want to take back. No one is different in that."
It's unclear if or when that time will come for Mickelson to make his PGA Tour return. However, he won't be back this week in Tulsa, Oklahoma.
McIlroy, who hasn't won a PGA Championship since 2014, will tee off alongside Tiger Woods and Jordan Spieth on Thursday morning.