Serena WilliamsWimbledon and U.S. Open champion, Serena Williams has withdrawn from an exhibition event against top-ranked Victoria Azarenka scheduled for this month in Thailand after having surgery on her toes.

A medical certificate from Florida podiatrist Jeffrey Rockefeller says Williams “was treated for a chronic foot disorder which involved minor procedures on both of her great toes.” He said she needs to minimize activity to fully recover.

However, Serena’s agent, Jill Smoller, said in an email today that the operation was “very minor” and won’t affect her preparations for the new tennis season. The Australian Open, the season’s first major championship, starts Jan. 14 in Melbourne.

Serena was replaced by Li Na for the exhibition on Dec. 29 in Hua Hin.