Wimbledon finalist Nick Kyrgios was beaten in his first singles match since October after having knee surgery.
The Australian, 28, lost 7-5 6-3 to China’s Wu Yibing in the opening round of the Stuttgart Open in Germany.
Elsewhere, American Venus Williams’ return to grass-court action ended in defeat by Celine Naef at the Libema Open in the Netherlands.
The 42-year-old former world number one lost 3-6 7-6 (6-3) 6-2 to Naef, 25 years younger at 17 years old.
Williams was making her first competitive appearance since the Auckland Open in January, where she reached the last 16 before losing to China’s Zhu Lin.
Williams has won seven Grand Slam singles titles – Wimbledon on five occasions and the US Open twice.
Kyrgios had not competed this season after having surgery to repair a small tear in his left lateral meniscus in January.