High-profile names were eliminated from both the Birmingham Classic and the Mallorca Open, with Naomi Osaka bowing out injured.
Marin Cilic will face Sam Querrey in the last eight at Queen's Club after the latter dumped out three-time major winner Stan Wawrinka.
Dominic Thiem had been on course for a semi-final meeting with Roger Federer in Halle, but he went down to Yuichi Sugita on Wednesday.
Simona Halep is set to go into Wimbledon without any competitive action under her belt on grass after pulling out of Eastbourne.
Andy Murray is not ruling anything out when asked if he will play in his home grand slam at Wimbledon.
The Tennis Anti-Corruption Program has seen Nicolas Kicker, of Argentina, banned for three years and fined for match-fixing offences.
There were contrasting results for two of the big names at the Gerry Weber Open, as Roger Federer progressed with ease.
Two previous Wimbledon champions prepared for this year's tournament with first-round wins at the Birmingham Classic on Tuesday.
Queen's Club welcomed back home favourite Andy Murray, but he could not join Grigor Dimitrov and Novak Djokovic in the second round.
Former world number one Andy Murray was handed a lengthy test on his return, losing to Nick Kyrgios but showing flashes of his quality.
If he beats Nick Kyrgios in the Stuttgart Open, Roger Federer will return to world number one. But he is not feeling the pressure.
Victory over Guido Pella at the Stuttgart Open left Roger Federer one win away from returning to world number one.
Alison Riske was unable to take seven chances to beat Coco Vandeweghe, who advanced to the semi-finals in the Netherlands.
After almost a year out injured, Andy Murray will make his return to competitive tennis at the Fever-Tree Championships.
An exciting Stuttgart Open semi-final with Roger Federer remains on the cards for Nick Kyrgios after a winning singles return.
The top seed, the defending champion and the British number one all progressed to the quarter-finals at the Nottingham Open on Thursday.
Karolina Pliskova lost to Magdalena Rybarikova at Wimbledon last year and fell to the unseeded Slovakian again in Birmingham.
It did not take Roger Federer long to get back to winning ways, as he clinched the Stuttgart Open on his return to action.
Dominic Thiem won his first match since the French Open final, getting past Mikhail Youzhny in the first round in Halle.