(REUTERS) - Phil Mickelson's quest to complete a career Grand Slam seems certain to have to wait another year after his decision to skip the US Open in two weeks' time.

Mickelson, six times a runner-up at the only Major championship he has not won, said on Saturday that he would miss this year's tournament to attend his daughter Amanda's high school graduation.

The ceremony will be held in southern California during the first round of the US Open at Erin Hills in Wisconsin on June 15.

Mickelson has not officially withdrawn, but it seems only a first-round weather washout could allow him to participate.

The 46-year-old confirmed his decision to reporters after the third round of the Memorial tournament in Dublin, Ohio.