Australian teenager Bernard Tomic emerged as a Wimbledon worry after being forced to retire towards the end of the first set of his first round match against Tommy Haas at the Gerry Weber Open in Halle.
The 19-year-old had been relishing his return to grass after becoming the youngest player since Boris Becker to reach the quarter-finals at the All England Club last year, where he lost to eventual champion Novak Djokovic.
But there must now be some concern over Tomic's fitness after he was forced to call it a day after just 22 minutes when he trailed 5-2, citing a sickness bug he has been battling since exiting the French Open last week.
Spanish sixth seed Marcel Granollers made a winning start with a 6-4 6-2 win over German qualifier Mischa Zverev, while veteran Radek Stepanek surprised seventh seed Andreas Seppi 7-6 (8/6) 7-6 (9/7).
Home favourite Florian Mayer got started with a 6-4 6-4 win over American Tim Smyczek, Serbia's Viktor Troicki beat another German, Benjamin Becker, 6-2 7-6 (8/6), and Lukas Lacko beat qualifier Konstantin Kravchuk 2-6 6-2 6-3.