Nick Kyrgios' return to action after seven months out with a knee injury has ended with a worrying defeat, after the 2022 Wimbledon finalist struggled with his mobility on court.
The Australian was beaten 7-5 6-3 by China's Yibing Wu in the first round in Stuttgart, the match lasting just 68 minutes.
While his serve was firing well, despite four double faults, Kyrgios appeared reluctant to chase balls around the court and by the end was visibly troubled by his knee.
During the changeover after the third game of the second set Kyrgios could be overheard saying to his team, 'I feel my knee every point. I can't walk without pain', before putting his head in his hands.
The world No.25 soldiered on and did not call for the trainer, but continued to look troubled and hobbled off after the match.
'Be patient with me my fans please,' Kyrgios tweeted after Tuesday's match.
'It's a process to get back to where I was. I know it's hard for you to see me perform like today, but I need more time and hopefully can get back to where I was.'
Ranked 64 in the world, Wu was not an easy draw for the eighth seed, despite it being the Chinese player's first senior match on grass.
His last competitive outing on the surface came in the juniors in 2017.
Kyrgios began well, showing his trademark flair and serving powerfully. At 5-5 he forced a break point, but Wu saved with an ace.
The Australian, who had begun to look uncomfortable midway through the set, seemed to make little effort to regain the advantage as his opponent held.
Serving to stay in the set, Kyrgios aced twice but also double-faulted twice as he was broken.
The second set went with serve to 3-4 but Kyrgios, a two-time semi-finalist in Stuttgart, was then broken to love, misjudging the game-winning point which he let go only for it to land inside the baseline.
Wu served out to love to complete victory.
It was Kyrgios' first tour-level singles match since October - though he made a big-money exhibition appearance in Saudi Arabia in December.
That was followed by surgery on a meniscus tear on his left knee - 'quite a serious surgery', he said before his match versus Wu.
With Wimbledon looming next month Kyrgios was keen to get grasscourt practice, but his priority now will be assessing his fitness.
Kyrgios also tweeted 'why are there no carpet tournaments' in the lead up to his defeat at the hands of Wu in Germany.
Also in the Stuttgart Open, Australia's Chris O'Connell beat Daniel Altmaier of Germany 6-3 6-1 to book a second-round tie with Italy's Lorenzo Sonego.