Former world number one Serena Williams has withdrawn from next week's WTA tournament in Montreal citing "personal reasons," organizers said Saturday.

"Of course, we are disappointed that Serena will not be joining us," tournament director Eugene Lapierre said in a statement, noting that despite the 23-time Grand Slam winner's absence, all of the top 10 players in the world are in the draw for one of the key tuneups for the US Open.