Australian Open champion Victoria Azarenka pulled out of the tournament on Tuesday, citing a foot injury.
Williams, who replaced her in the No.1 spot despite losing the final of the Qatar Open in Doha, then withdrew with a lower back injury just minutes before she was due on court for a second-round match against Frenchwoman Marion Bartoli in Dubai.
When players are forced out of a tournament through injury, they can usually replace the ranking points lost with those from a different tournament.
However, despite both players providing requisite medical documentation, the WTA has decided the week will be a "zero-pointer" in the two players' ranking totals.
Azarenka will lose $100,000 (£66,000) from her potential share of the end-of-season bonus pool while Williams will be deprived of $50,000 (£33,000).
The top 10 players share a bonus fund of $4.9m (£3.2m) when the season finishes.
The Dubai tournament is one of the top eight events on the WTA Tour outside the Grand Slams.
Tournament sponsor Dubai Duty Free is a key partner of the governing body.
Tournament director Salah Tahlak said their withdrawals were "disappointing both for the tournament and for the fans, some of whom come from all over the world to see them play".