Mickelson missed the first four events of LIV's 2026 season due to the same family health matter and had just returned to action on the Saudi-backed circuit two weeks ago in South Africa where he finished in a share of 48th.
"Unfortunately, I will not play in the Masters Tournament next week and will be out for an extended period of time as my family continues to navigate a personal health matter," the six-time major champion said in a statement posted on X.
"I have great respect for Augusta National Golf Club and it is definitely the most special week of the year. I wish everyone the best of luck and will be watching."
This marks the first time Mickelson will not compete in the year's first major since 2022, when he sat out the tournament while taking a self-imposed break after excerpts from an unauthorised biography revealed he had called the Saudis "scary" but was willing to look past their human rights record.
Mickelson missed the cut at last year's Masters.
The Masters is scheduled for April 9-12 at Augusta National Golf Club.