Stefanos Tsitsipas' toils were worsened on Wednesday by a straight-sets loss to Pierre-Hugues Herbert in the Shenzhen Open.
The world number 15's run to last month's Rogers Cup final - where he was beaten by Rafael Nadal - prompted many to suggest he has a bright future in the game.
But since that Masters 1000 event, the Greek has won just one of five matches, in the US Open first round against Tommy Robredo.
As the second seed in Shenzhen, Tsitsipas enjoyed an opening bye in the ATP 250 tournament but fell at the first hurdle as Herbert prevailed 6-3 7-6 (7-4) to book a quarter-final meeting with Albert Ramos-Vinolas, a 7-6 (7-4) 4-6 7-6 (7-3) winner over Viktor Troicki.
Yoshihito Nishioka sprung a surprise with a 7-6 (7-5) 3-6 7-5 defeat of sixth seed Denis Shapovalov and the world number 171 advances to face Cameron Norrie, who eventually converted his sixth match point to seal a shock 6-4 7-6 (10-8) win over third seed Borna Coric.
In the Chengdu Open, Bernard Tomic fought off a match point to come through 7-6 (7-5) 2-6 7-6 (8-6) against Lloyd Harris. Tomic's next challenge comes in the form of Felix Auger-Aliassime, who stunned world number 23 and second seed Hyeon Chung 7-6 (7-2) 5-7 6-4.
Seventh seed Joao Sousa came from behind to defeat Vasek Pospisil 6-7 (4-7) 6-4 7-6 (7-0) while there were also wins for Malek Jaziri and Matteo Berrettini.
