Victoria Azarenka has claimed that it was "really obvious" that she had to pull out of the Miami Masters with an ankle injury.

The world number one was forced to withdraw from the tournament shortly before her second-round encounter with American Madison Keys on Friday.

Azarenka recently missed a quarter-final against Caroline Wozniacki in Indian Wells with the same problem.

"The decision was really hard to make," Azarenka is quoted as saying by Tennispanorama.com. "In one case, it was really hard to make. In the other case, it was really obvious what the decision was couple days ago already."

Azarenka was replaced by lucky loser Lauren Davis, who went on to defeat fellow American Keys in three sets.