Serena Williams and Victoria Azarenka penalised for failing to fulfil Dubai duties

Victoria Azarenka: The former world No 1 was fined $100,000 for missing the Dubai event (Reuters)

Serena Williams and Victoria Azarenka will pay financial and ranking points penalties following their late withdrawals from this week's Dubai Duty Free Championships.

Although the current and former world No 1s provided the requisite medical documentation the Women's Tennis Association has deducted $100,000 (about £66,000) from Azarenka's potential earnings from the end-of-year bonus pool and $50,000 from Williams' possible share of the pot. The top 10 players share a bonus fund of $4.9m (£3.2m) at the end of the season.

The WTA has also decreed that this week's tournament will count as a "zero-pointer" in the two players' ranking totals, which means that they cannot replace it with points from a different tournament. Azarenka, citing a foot injury for this event, and Williams, who said she had a back problem, both played in Doha last week.

Azarenka pulled out from this week's tournament on Tuesday and Williams withdrew not long before she was due to play her first match the following day. The tournament, which offers $2m in prize-money, is one of eight "premier" events, which are the most important on the WTA tour, and had attracted 17 of the world's top 20 players.

Dubai Duty Free, which owns and organises the tournament, has sponsored the WTA for nine years and is one of the governing body's six main partners.

Salah Tahlak, the tournament director, who spoke to a WTA official in Florida, said the withdrawal of the two top seeds was "disappointing both for the tournament and for the fans, some of whom come from all over the world to see them play".

Today's semi-finals will pit the Czech Republic's Petra Kvitova against Denmark's Caroline Wozniacki, while Sara Errani will face fellow Italian Roberta Vinci. Kvitova, who has been in good form since the Australian Open, beat Agnieszka Radwanska, the world No 4 and highest-ranked player left in the field, 6-2, 6-4. Wozniacki beat Marion Bartoli 4-6, 6-1, 6-4 after which the Frenchwoman revealed that she is to be coached by Amélie Mauresmo. Bartoli said she would be working hard to improve her physical condition. "I'm ready to make all the sacrifices,' she said.

Britain's Heather Watson went out in the quarter-finals in Memphis, beaten 6-1, 6-2 by Switzerland's Stefanie Voegele.