Serena Williams, who won the Australian Open in 2017 while pregnant with daughter Alexis Olympia, returns as the 16th-seeded player after missing last year's tournament.
It was Halep's first match since October after a lengthy layoff due to a herniated disc in her back.
It will be the first time Halep has played since the French Open champion ended her season in October due to a herniated disc in her back.
Djokovic, recognized by the ITF for the sixth time, won the Wimbledon and U.S. Open titles a year after undergoing surgery on his right elbow.
Apart from Halep, only four women have been named Fan Favourite in the ten-year history of the award.
Caroline Wozniacki of Denmark retained the third sport in this week's unchanged top 10, ahead of Ukraine's Elina Svitolina and Japan's Naomi Osaka.
Halep's withdrawal means Kiki Bertens has qualified for the final spot, joining Angelique Kerber, Naomi Osaka and many others.
The 27-year-old Halep had her best year on tour in 2018, reaching the Australian Open final and then winning her first Grand Slam title a few months later at Roland Garros.
Halep lost the first set 6-1 to Tunisia's Ons Jabeur before retiring with a back injury that she also had problems with at last week's Wuhan Open.
Halep lost the first set 6-1 to Tunisia's Ons Jabeur before retiring with a back injury that she also had problems with at last week's Wuhan Open.
Halep was beaten 6-2, 6-4 by 44th-ranked Kaia Kanepi of Estonia on Monday in a match that was stunningly lopsided and lasted all of 76 minutes.
The top in both the WTA and ATP rankings remain unchanged with all the players holding on to their spots.
Djokovic overcame an upset stomach and a sluggish first set Wednesday, beating Adrian Mannarino 4-6, 6-2, 6-1 before heavy rain halted afternoon matches at the Western & Southern Open.
Despite playing on only 15 hours rest, Halep was in control from the outset against the 15th-seeded Barty, eliminating the Australian in 71 minutes.
Germany's Angelique Kerber kept world No.4, after having claimed the spot a week earlier thanks to her first-ever Wimbledon title victory.
The top-seeded Halep's exit means only one of the women's top-10 seeds remains in the tournament, Pliskova, which leaves Serena Williams as the big favourite to win her eighth Wimbledon title.
Halep has not played since beating Sloane Stephens for the Roland Garros title earlier this month.
Rafael Nadal and Simona Halep became the first pair of ATP and WTA No 1s to both win the title at Roland Garros since Jim Courier and Monica Seles in 1992.
Simona Halep beat Sloane Stephens 3-6, 6-4, 6-1 for her first Grand Slam title.
Halep added Grand Slam trophy No. 1 to her No. 1 ranking, coming back from a set and a break down to beat Sloane Stephens 3-6, 6-4, 6-1.
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