STUTTGART, Ger - Top seed Naomi Osaka is in line to face in-form Hsieh Su-Wei in the second round of the Porsche Tennis Grand Prix, but a potential quarterfinal against Angelique Kerber has been shelved.

Simona Halep's withdrawal from the competition means that the two-time champion now occupies the No.2 seed slot at the bottom of the draw, with her place taken by lucky loser Giulia Gatto-Monticone, who now face Donna Vekic in the first round.

GALLERY: Stuttgart sensations: Previous winners

If the seedings and rankings are respected, it means that Elise Mertens is in line to face the US and Australian Open champion in the last eight. 

The WTA World No.1, the youngest player in the draw, could potentially have to overcome Hsieh, the eldest, in the last 16 after being given a bye from the opening round. The Taipei player takes on fellow tournament debutant Qiang Wang first up.

Osaka is making her second appearance at the tournament, having previously featured in 2017, where she made a first-round exit to Johanna Konta.

Kerber, who last won the title in 2016, now finds herself in the same quarter as Kiki Bertens, with the German's first match against either qualifier Sara Sorribes Tormo or compatriot Andrea Petkovic, who is a wildcard.

Meanwhile, Garbiñe Muguruza's withdrawal on Tuesday means that Victoria Azarenka will face Vera Zvonareva in the first round. 

The winner of that tie will face No.4 seed and defending champion Karolina Pliskova, who reached the final in Miami earlier this month.

In the same quarter, unseeded Caroline Garcia takes on Anett Kontaveit, the eighth seed who reached a career-high ranking of WTA World No.14 this month after making the last four in Miami. The bottom half of the draw includes Jelena Ostapenko taking on Anastasija Sevastova in an all-Latvian opener, with third seed Petra Kvitova a potential quarterfinal opponent.

Five of the Top 10 players in the world are taking part in Stuttgart this week, including Osaka, Kvitova, Pliskova, Kerber and Kiki Bertens. 

Simona Halep could face Andrea Petkovic in the second round (©Jimmie48/WTA)

Maria Sharapova, Sloane Stephens and Elina Svitolina are among the players to have withdrawn from the tournament through injury. Pliskova overcame CoCo Vandeweghe 7-6, 6-4 to take last year's title.

GALLERY: This year's 18 different champions

The 18 WTA tournaments so far this year have provided a record 18 different winners, with eight of those taking part in Germany this week. Pliskova, Julia Goerges, Kvitova, Osaka, Bertens, Elise Mertens, Belinda Bencic and Muguruza will all be bidding to become 2019's first multiple champion.

First round draw
[1] N Osaka (JPN) - Bye
Q Wang (CHN) v S Hsieh (TPE)
E Mertens (BEL) v D Kasatkina (RUS)
D Vekic (CRO) v [5] A Kerber (GER)
[4] K Pliskova (CZE) - Bye
G Muguruza (ESP) v V Azarenka (BLR)
A Pavlyuchenkova (RUS) v J Goerges (GER)
C Garcia (FRA) v [8] A Kontaveit (EST)
[7] A Sevastova (LAT) v J Ostapenko (LAT)
L Tsurenko (UKR) v [WC] L Siegemund (GER)
Qualifier v [WC] D Cibulkova (SVK)
[3] P Kvitova (CZE) - Bye
[6] K Bertens (NED) v Qualifier
Qualifier v B Bencic (SUI)
Qualifier v [WC] A Petkovic (GER)
[2] S Halep (ROU) - Bye