The Dubai Open lost its second leading seed in as many days as Serena Williams pulled out less than 30 minutes before she was due to have taken to the court for her opening match on Wednesday.

The American, who has never hidden the fact that she plays to her own rhythm and makes a tournament schedule to suit herself, claimed a lower back problem.

On Tuesday, Williams, who regained the number one ranking from Victoria Azarenka last week, said she was eager to play and cement her return to the top of the rankings.

On Tuesday, Azarenka, originally the top seed, pulled out for the second year in a row, with what she called a foot problem – the same injury she claimed in 2012 with a similar withdrawal at the last minute.

Williams was to have opened in the second round after a bye against France’s Marion Bartoli.