DOHA, Qatar — Dinara Safina has retired with an injury against Jelena Jankovic in her first round-robin match at the Sony Ericsson Championships.

She will lose her No. 1 ranking to Serena Williams if she has to pull out of the tournament in Doha, Qatar.

Safina was serving at 1-1 in the first set Wednesday when she stopped play, walked over to her chair and covered her face with a towel. She told the chair umpire she could not continue. The nature of the injury was not immediately clear.

Safina's margin over Williams is so slim that the player who performs best in Doha will end the year as No. 1. Williams won her first match Tuesday.

The tournament features the top eight players in the world, with a group stage before the semifinals.