Wife Steffi Graf -- no slouch on the court, either -- needed three stitches to close the wound made when Agassi's racket caught her on the lip, the Houston Chronicle said Monday.
The two were shagging tennis balls with some children during an Oprah Winfrey-sponsored reality show, which netted about $300,000 for a La Marque, Texas, elementary school to use for supplies and upgrades.
"She's OK," Agassi said. "It was an unfortunate accident."
In a twist, Stefan Krenzer, the doctor who stitched Graf up, had just won the opportunity to visit Las Vegas for a tennis lesson from Agassi and Graf.
Details of the reality show, "The Big Give," are not being revealed but this segment involved a fundraising competition between Agassi and skateboarder Tony Hawk, who was raising money for a school in Freeport, Texas.
"It's a show about believing in the best of the human spirit," Agassi said.