Novak Djokovic was hit on the head by a water bottle as he signed autographs after his win at the Italian Open.
A video on social media showed world number one Djokovic falling to the floor after being hit by the object, which came from the stands.
Tournament organisers said the hard bottle had fallen out of the bag of someone in the crowd.
The 24-time Grand Slam champion stayed on the ground for a while before being helped out of the arena in Rome by security.
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“This is not being treated as a deliberate act, but as an accident,” said tournament organisers in statement reported by PA.
“A boy was calling out to get an autograph and the bottle fell out of his bag.
“Novak has undergone the necessary checks and has already left to return to his hotel. His condition is not a cause for concern.”
A further video was posted that seemed to show a fan leaning over to get an autograph, with the bottle slipping out of his rucksack.
The incident happened as Djokovic approached supporters in the stands following his 6-3 6-1 win over France’s Corentin Moutet.
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He was signing a sheet of paper for a fan when the water bottle struck him on the top of the head.
Djokovic is due to play Chile’s Alejandro Tabilo on Sunday in the next round.
Boutler beaten by Slovakian qualifier
Katie Boulter was knocked out in the second round of the women’s singles in Rome after a 6-4 7-6 (10-8) defeat to Slovakian qualifier Rebecca Sramkova.
Boulter – seeded 26th for the tournament – was broken twice by the world number 120 early in the first set as she struggled for rhythm.
The British number one managed to steal a break back but Sramkova was able to close out the first set.
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Boulter fought back from two breaks down in the second set but squandered an opportunity to square the match when she was 5-4 up.
The 27-year-old saved three match points in the tie-break before Sramkova came out on top in two hours and seven minutes.
In the men’s doubles, Jamie Murray and Michael Venus wrapped up a 6-4 6-3 victory over Lloyd Glasspool and Jean-Julien Rojer to reach the second round.
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Heather Watson and Xu Yifan suffered a first-round exit in the women’s doubles after a 6-3 1-6 10-8 defeat to Zheng Saisai and Wang Xinyu.
