Ochoa took over from Sorenstam as world number one last year
World number one Lorena Ochoa withdrew from this week's Annika Sorenstam-hosted Ginn Tribute event on the LPGA Tour because her uncle is ill.
Ochoa travelled to her native Mexico on Tuesday, putting the duel with the former top-ranked Sorenstam on hold.
"I am very sorry to have to withdraw," Ochoa said. "I need to be with my uncle and my family right now."
Sorenstam said: "She is a tremendous ambassador for our game and we will miss her this week."
She added: "That being said, family comes first and I know she has a very close family. I respect and support her decision and wish them the best."
Ochoa took over the top spot from the injury-ravaged Sorenstam last year, but the fit-again Swede has vowed to bounce back before retiring at the end of the season.
Mexico's Ochoa has won six of 13 LPGA events this season to Sorenstam's three.
Leta Lindley, who won the Corning Classic last week, said Ochoa, last year's runner-up to Nicole Castrale, will be missed at RiverTowne Country Club.
"But I guess that leaves a little bit more money for everybody else, the way she's been playing this year," Lindley said.
Last year, teenager Michelle Wie withdrew from the Ginn Tribute after playing 16 holes of her opening round, citing a wrist injury.
She was playing poorly at 14-over and two shots away from being banned from tour exemptions until the following season for shooting an 88 or higher.
Wie was not offered, nor did she seek, an exemption for the tournament this year.
Instead, she will make only her third competitive appearance of the year at this week's German Open on the Ladies European Tour.