Injured Serena out of Monterrey tournament

US star Serena Williams has pulled out of the Monterrey WTA tournament next week citing a niggling ankle injury, event organisers said on Sunday.

The former world number one had received an invitation for the tournament which starts on Monday.

But organisers said they had received a statement from the WTA saying that the 30-year-old would not be able to accept the invitation. The world number 12 will however play an exhibition match against Argentine Gisela Dulko on Sunday.

Williams has only competed in two tournaments this year and withdrew before her Brisbane quarter-final match because of a left ankle injury.

She won both her two singles ties as the United States crushed Belarus 5-0 in their Fed Cup World Group-II clash in New York earlier this month.