Phil Mickelson has signalled his intention to miss the US Open to attend his daughter's graduation.
Speaking before his third round at the Memorial Tournament, the 46-year-old said daughter Amanda's graduation would take precedence over the only major championship to have eluded him.
This year's event runs from June 15-18 at Erin Hills.
Mickelson has notified tournament officials of his intention, but has yet to withdraw formally, making provisions for last-minute changes of plan. Tournament rules dictate he has until just before the commencement of his opening round to pull out.
"My daughter is graduating, she is the school president, she'll be giving the commencement speech for the school and I am going to be there," he said at a media conference.
"Unfortunately it comes on the Thursday of the Open, around 10 in the morning pacific time and there's no way I can make it no matter what the tee time is. I didn't want the USGA (US Golf Association) to be caught off guard and I wanted the alternate to know he will most likely be in.
"There is no sense in doing it (withdrawing formally) now. Something might come up with the commencement, the weather, something unforeseen, but it doesn't look very good. I wanted to make sure they had enough notice.
"It doesn't look good for me playing but I am really excited about this moment in our family's life."
In a statement, the USGA said: "Phil called to say because of the timing of his daughter's high school graduation, he would likely not be able to play in the US Open at Erin Hills. We applaud and appreciate the fact that he is being pro-active so that the USGA can make any appropriate adjustments should he not be able to play.
"We certainly understand and support that Phil's family commitments are of paramount importance, and hope that the timing will work in his favour."
Despite failing to win the US Open, five-time major winner Mickelson has finished second or been tied for second on six occasions.