Defending men’s champion Kei Nishikori and five-time Grand Slam winner Maria Sharapova have pulled out of the Hawaii Open that starts tonight at the Stan Sheriff Center.

Nishikori said at a tournament-opening press conference today that he won’t be playing because of a nagging elbow injury. At the same gathering, a spokesman said Sharapova is out due to “unforeseen circumstances.”

Three-time Hawaii high school state champion Alyssa Tobita is replacing Sharapova. No replacement was named for Nishikori.

“I’m just thankful for the opportunity and am going to make the best of it,” said Tobita, a Mililani and Oregon alumna who is a first-year professional player.

“I’m disappointed to announce my withdrawal from the Hawaii Open. I find myself needing a little more time and preparation before my first tournament back,” Sharapova said, in a statement provided by tournament officials after the press conference. “I wish I could be there to see my fans who were coming to watch me play.”

Said Nishikori, also in a statement from the tournament: “Unfortunately I have to pull out of the Hawaii Open this year. I am not 100% ready yet,” Nishikori said. “It is very disappointing as I love coming here. … I look forward to meeting tennis fans here this week.”

The event runs through Saturday.